De-en Jiang, University of California, Riverside
Dongil Lee, Yonsei University
Yuichi Negishi, Tokyo University of Science
Jie Zheng, The University of Texas at Dallas
Symposium Support World Gold Council
PP2: Gold Catalysis
Tuesday PM, April 07, 2015
Marriott Marquis, Yerba Buena Level, Salon 2/3
2:30 AM - *PP2.01
Controlled Synthesis of Nanostructured Au Catalysts
Sheng Dai 1 2
1Oak Ridge National Laboratory Oak Ridge United States2University of Tennessee Knoxville United StatesShow Abstract
Catalysis is critically important to energy production and to meeting the environmental quality mission of promoting the development and utilization of clean, efficient, and reliable energy resources. It is essential to understand the relationships between the atomic and nanoscale structure of metal nanoparticles and catalyst supports and the crucial role these play in promoting or altering catalytic pathways. The key focus of this talk lies in the controlled synthesis of metallic Au catalysts with unique metal-support interactions and nanostructured nonmetallic catalysts for heterogeneous catalysis. Critical issues and emerging science and technology in heterogeneous catalysis will be discussed in context of controlled synthesis.
Acknowledgement: This work was performed at the Oak Ridge National Laboratory and the University of Tennessee and supported by the U.S. Department of Energy&’s Office of Basic Energy Sciences under contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.
3:00 AM - PP2.02
Tailoring Gold-Copper Anisotropic Nanostructures for Plasmonic Enhanced Catalysis
Jingyi Chen 1 Shutang Chen 1 Samir Jenkins 1 Cameron Crane 1
1University of Arkansas Fayetteville United StatesShow Abstract
Bimetallic nanoparticles possess catalytic properties different from those of constituent metals or simple mixtures, and often exhibit enhanced catalytic activity. Gold-based bimetallic materials integrate additional function to the catalysts because their strong interaction of light and open up the opportunities for plasmonic enhanced catalysis. When the optical “hot spots” overlap with the catalytically-active sites, one can expect tremendous enhancement of the catalytic activity under the optical resonance condition. In this work, we develop a kinetic-control seeded growth method to synthesize anisotropic gold-based materials, specifically, gold-copper nanorods for plasmonic enhanced catalysis. This approach uses gold nanoparticles as seeds, and subsequently reduces copper atoms on one side of the seeds, resulting in Janus nanoparticles with a gold-rich and a copper-rich portion. These Janus nanoparticles ultimately lead to the elongation of the nanoparticles into nanorods by retarding reduction kinetics of copper through galvanic replacement. The composition, crystal structure, and aspect ratio of the nanorods can be conveniently tuned by changing seed and precursor concentrations. A third metal such as platinum and palladium can be incorporated into the nanorods to form multi-metal anisotropic nanostructures. We compare the catalytic activity of these nanorods with different aspect ratio and crystal structures (alloy versus intermetallic) for the nitrophenol reduction and electro-oxidation of methanol. We demonstrate the plasmonic-enhanced catalytic activity of these nanorods upon irradiation of light. Mechanisms are further investigated by X-ray photoelectron spectroscopy and Raman spectroscopy.
3:15 AM - PP2.04
PdAu Single Atom Alloys for Activating Diatomic Molecules
Felicia R Lucci 1 E Charles H Sykes 1
1Tufts University Medford United StatesShow Abstract
Au based catalysts are widely studied due to their ability to catalyze selective reactions. Au catalysts, however, often exhibit low reactivity and are hindered by a low dissociation probability of small molecules. The activity can be enhanced by alloying Au with Pd, a more reactive but less selective catalyst. PdAu alloys are known to catalyze a wide range of hydrogenation and oxidation reactions; however, the size of Pd ensembles in Au required for small molecule activation is not well understood. Using scanning tunneling microscopy and temperature programmed desorption, we investigate the effect of the size of Pd ensembles in Au(111) on catalytic activation of H2 and O2. We show that isolated Pd atoms are capable of catalyzing the dissociative adsorption of H2, a process which was previously thought to require contiguous Pd sites. The unique energy landscape of H2 activation on the alloy results in an intermediate H2 desorption temperature (170 K) compared to Pd(111) (310 K) and Au(111) (110 K). Compared to the well characterized PdCu single atom alloys known for allowing H spillover, Au based alloys do not enable H spillover from the active Pd sites to Au. H atoms can be transported between single Pd active sites which is suggestive of the transient existence of H atoms on Au. Conversely, single Pd atoms are not capable of O2 dissociative adsorption. Small Pd clusters on Au enable O2 adsorption at Pd-Au interface sites. Weakly bound H and O atoms are capable of enhancing reactions on the Au substrate and the PdAu system serves as an ideal model system to probe selective hydrogenation and oxidation reactions via single reactive sites.
3:15 AM -
3:30 AM - *PP2.05
CO Oxidation on TiO2 Supported Gold Cage Clusters: Size, Shape, and Structural Flexibility Effects
Xiao Cheng Zeng 1 Lei Li 1 Hui Li 2 Yi Gao 3
1University of Nebraska-Lincoln Lincoln United States2Institute of Physics Beijing China3Institute of Applied Physics Shanghai ChinaShow Abstract
Bulk gold is known to be catalytically inert whereas gold nanoclusters on metal oxide support can exhibit exceptional catalytic properties towards CO oxidation. We have performed a comprehensive study of catalytic activities of sub-nanometer gold clusters, hollow-cage clusters in particular, supported by TiO2(110) surface using density functional theory calculations, Born-Oppenheimer molecular dynamics simulation, and micro-kinetics analysis. Our goal is to elucidate the importance in understanding the catalytic activity of subnanometer gold clusters with precisely controlled size and shape. We find that catalytic activities of the Aun/TiO2 systems increase with the size n up to 18, for which the hollow-cage Au18 isomer exhibits highest activity for the CO oxidation, with a reaction rate ~100 times higher than that of Au7/TiO2 system. In stark contrast, the pyramidal isomer of Au18 exhibits much lower activity comparable to the Au3-4/TiO2 systems. We will also show a Born-Oppenheimer molecular dynamics simulation evidence of the generation of oxygen vacancies at the hollow-cage Au16 and TiO2 (110) interface during CO oxidation. In this case, contrary to the conventional Langmuir-Hinshelwood (L-H) mechanism, the CO molecule adsorbed at the perimeter Au sites of Au16 tends to attack a nearby lattice oxygen atom on the TiO2 (110) surface rather than the neighboring co-adsorbed molecular O2. So this simulation provides real-time demonstration of feasibility of the Mars-van Krevelen (M-vK) mechanism as evidenced by the generation of oxygen vacancies on the TiO2 surface in the course of the CO oxidation. On the other hand, at the golden cage Au18 and TiO2 interface, the L-H mechanism is more favorable than the M-vK mechanism due to higher structural robustness of the Au18 cage. In summary, the selection of either M-vK or L-H mechanism for the CO oxidation seems depending primarily on the structural flexibility of the hollow-cage Au clusters on the TiO2 support.
4:30 AM - PP2.06
Carbon Monoxide Oxidation Catalyzed by Atomically Well-defined Gold Nanoclusters Supported on CeO2
Yuxiang Chen 1 Rongchao Jin 1
1Carnegie Mellon University Pittsburgh United StatesShow Abstract
Atomically well-defined gold nanoclusters protected by thiol ligands, referred to as Aun(SR)m, where n and m are specific numbers, exhibit quite unique catalytic activities compared to gold complexes and conventional gold nanoparticles. Thus far, gold nanoclusters have been demonstrated to have the capability of catalyzing a number of reactions in solution phase. As for the gas phase reactions such as carbon monoxide (CO) oxidation, supported Aun(SR)m nanoclusters on CeO2 also show intriguing catalytic properties. One of the most attractive features for nanogold catalyzed CO oxidation is the size dependent catalytic activity. However, conventional gold nanocatalysts usually have a non-uniform particle size distribution, which would make it difficult to correlate the catalytic performance with the size and structure of the catalyst. Herein, we select several gold nanoclusters whose structures have been solved by X-ray crystallography, including Au10(SR)10, Au25(SR)18, Au36(SR)24 and Au38(SR)24, as a paradigm system to systemically study the size and structure dependent behavior in CO oxidation with CeO2 supported Aun(SR)m nanoclusters as catalysts.
4:45 AM - PP2.07
Atomically Precise Au25 Nanocatalysts for Carbon Negative, Renewable Energy-Compatible Electrochemical CO2 Conversion
Douglas R. Kauffman 1 Christopher Matranga 1 Jay Thakkar 1 2 Rajan Siva 1 2 Rongchao Jin 2
1National Energy Technology Laboratory Pittsburgh United States2Carnegie Mellon University Pittsburgh United StatesShow Abstract
Converting waste CO2 into fine chemicals and/or fuels is an exciting prospect for green-house gas mitigation. Current CO2 conversion approaches include photo-, electro- and thermo-catalytic processes. Each approach has its benefits, but electrocatalytic CO2 conversion is a leading candidate because it operates at ambient conditions with extremely high reaction rates, product selectivity and faradaic efficiency, and it requires small energy input (several volts). Carbon balance is a major consideration for any CO2 conversion technology because the majority of the United States' electricity is derived from burning fossil fuels. This necessarily shifts most CO2 conversion technologies into the carbon positive regime, and CO2 produced from fossil-fuel derived electricity likely exceeds that consumed by the conversion process. This limitation is an important challenge that must addressed before CO2 conversion technologies can be implemented on an industrial scale. Here, we describe a “carbon negative” (more CO2 consumed than produced) electrochemical CO2 conversion system based on atomically-precise Au25 nanocatalysts. The catalytic system operates on inexpensive (ca. $10-20 USD), consumer-grade photovoltaic cells and solar-rechargeable batteries. We show stable CO2 → CO conversion activity with turnover numbers (TON: mol CO2/mol catalyst) surpassing 5x106, rates exceeding 800 L CO2 /gram catalytic metal/hour, and faradaic efficiencies and product selectivities around 90%. These performance metrics correspond to 1-2 kg CO2 converted per gram of catalytic metal every hour. We can also tune product selectivity to favor CO or H2 production by varying the catalyst loading and/or operating voltage. We show stable operation for 12 hours with photovoltaic cells to represent daylight operation, and 24 hours with a solar-rechargeable battery to mimic low-light or night-time hours. This study provides proof-of-principle example that renewable-powered electrocatalysis is a viable strategy for CO2 conversion applications.
5:00 AM - PP2.08
Electrochemical Properties of Bimetal Nanoclusters and their Electrocatalytic Applications
Kyuju Kwak 1 MinSeok Kim 1 Dongil Lee 1
1Yonsei University Seoul Korea (the Republic of)Show Abstract
Thiolate-protected gold nanoclusters doped with foreign metal atoms have received considerable research interest in recent years. Doping of gold nanoclusters has drastic effects on their optical, electrochemical and catalytic properties, which can open up new avenues in their use in catalysis, sensing and biomedical applications. In this presentation, we report electrochemical properties of thiolate-protected Au25 nanoclusters doped with Ag, Cu, Pt and Pd. Voltammetric investigations of the doped nanoclusters showed that redox potentials of gold nanoclusters are significantly altered by doping with foreign metal atoms. The electrocatalytic activities of the doped gold nanoclusters were examined by monitoring electrochemical reduction of azobenzene at doped gold nanocluster-modified electrodes. Dramatic mediated catalytic effect was observed with gold nanoclusters doped with Pt and Pd. This effect can be ascribed to the doping-induced tuning of the redox potentials and enhanced electrocatalytic activity of the doped gold nanoclusters.
5:15 AM - PP2.09
Structural Evolution of AuPt and AuPd Nanoparticles Fabricated by Microwave Assisted Synthesis: A Comparative Study
Tirtha Som 1 Robert Wendt 1 2 Simone Raoux 1 Jean L Jordan-Sweet 3 Markus Wollgarten 1 Klaus Rademann 2
1Helmholtz Zentrum Berlin fuuml;r Materialien und Energie Berlin Germany2Humboldt University Berlin Berlin Germany3IBM T. J. Watson Research Center New York United StatesShow Abstract
Bimetallic nanoparticles (NPs), particularly Au/Pt and Au/Pd, have attracted extensive attention due to their wide-spread application in catalysis, optoelectronics and energy recuperation. Here we have attempted the fabrication of Au/Pt and Au/Pd bimetallic NPs by an energy-efficient eco-friendly microwave methodology. The microwave-assisted reactions enable considerably large product yields over conventional colloidal methods due to (a) almost two-fold increased reaction kinetics, (b) localized superheating at reaction sites and rapid rise of initial temperature. Au NPs (sizes 20 ± 3 nm) are fabricated in the first step followed by the reduction of [K2PtCl6] or [PdCl2(NH3)2] in tetraetylene glycol at 180 0C for 2 min. Controlling and understanding the atomic structure and elemental distributions of these NPs are crucial for their optimized performances. So, we also address the fundamental question of the most likely arrangement of Au and Pt or Pd atoms in these bimetallic NPs prepared under similar conditions by complementary characterizations using UV-Vis spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The UV-Vis spectroscopy reveals the formation of an alloy shell. The extent of depression of the plasmon peak of Au and its blue-shift reveals substantial deposition of Pd atoms on an Au core and significant alloying in comparison to Au/Pt NPs. XRD reveals the gradual shift of the diffraction peak from the position of Au to the position of Pt or Pd with change in composition. XRD supports the formation of a thick alloy shell in these NPs. However, the TEM images reveal a very interesting result. With increase in Pt concentration, the size of the dispersed NPs decreases from 20 ± 3 nm to about 16 nm (± 1 nm) and there is evolution of a bimodal particle size distribution with small particles about 1-2 nm diameters. On the contrary, with increasing Pd concentration, the particle size of the dispersed particles increases to about 32 nm (± 1 nm). This discrepancy of particle size evolution for the two systems arises due to the differences in surface energies (Pt > Pd > Au atoms). Pt atoms tend to diffuse towards the core with the formation of Au nano-islands which eventually segregates leading to a reduction in particle size and bimodal distribution. At higher concentration of Pt, Pt and Au atoms tend to nucleate separately also contribution to bimodal distribution. While for Au/Pd NPs, we have an Au core with an alloyed shell having higher Pd concentration. This is further supported by experimental evidence by selective etching and dissolution of Au by potassium-iodide solution. Furthermore, the AuPd bimetallic NPs are found to posses better catalytic activities in the reduction of 4-nitrophenol to 4-aminophenol than AuPt and monometallic NPs.
References  R. Ferrando, et al Chem. Rev. 2008, 108, 845.  N. Dahal et al ACS Nano 2012, 6, 9433.
Tuesday AM, April 07, 2015
Marriott Marquis, Yerba Buena Level, Salon 2/3
9:00 AM - *PP1.00
Plamon-Enhanced Spectroscopy of Gold Nanostructures with Ultrathin Insulation Shells
Jian-Feng Li 1 Zhong-Qun Tian 1
1State Key Laboratory of Physical Chemistry of Solid Surfaces and College of Chemistry and Chemical Engineering, Xiamen University Xiamen ChinaShow Abstract
Surface-enhanced Raman spectroscopy (SERS) yields fingerprint vibrational information with ultra-high sensitivity up to single molecule level. When light of a resonant wavelength is incident upon gold nanostructures, it initiates surface plasmon resonance (SPR) that gives narrow regions of enhanced electromagnetic field strength, reshaping the incident laser dramatically. For widely extending the practical application of SERS, we adopted a “borrowing” strategy and rationally designed several kinds of gold nanostructures with controllable ultrathin shells, such as Au@SiO2 nanoparticles, which is named “shell-isolated nanoparticle-enhanced Raman spectroscopy” or “SHINERS”. Here, the Au cores act to support SPR modes and boost electromagnetic field (EM) strength in localized regions at the interface. The ultrathin (2-5 nm) yet pinhole-free silica shells isolates the core from its chemical environment, but allow the EM field generated by the gold cores to probe that the surface and the environment. This method has been applied to a number of challenging systems, from metal single-crystal surfaces to semiconductors, from live cells to residue pesticides on fruits and vegetables.
These Au core-shell nanostructures with controllable ultrathin insulation shells are sensitive and uniquely suitable to provide a wealth of information about adsorption and reaction processes occurring at the surfaces, and to understand the correlations that exist between structure and reactivity for a wide range of interfacial phenomena. Recently we have extended the concept of shell-isolated gold nanoparticle-enhancement to several optical spectroscopies such as fluorescence, infrared absorption and sum frequency generation, showing great potential of plamon-enhanced spectroscopy of gold nanostructures with ultrathin insulation shells, which will be discussed in details.
1. Jian-Feng Li et al., Nature, 2010, 464, 392-395.
2. Jian-Feng Li et al., Nature Protoc., 2013, 8, 52-65.
3. Zhong-Qun Tian, Bin Ren, Jian-Feng Li, Zhi-Lin Yang, Chem. Commun., 2007, 3514-3534.
4. Jian-Feng Li, Zhong-Qun Tian, in Frontiers of Surface-Enhanced Raman Scattering: Single Nanoparticles and Single Cells, eds. Y. Ozaki, K. Kneipp, R. Aroca, WILEY; Chichester, 2014, pp163-192.
PP3: Poster Session: Poster Session I
Tuesday PM, April 07, 2015
Marriott Marquis, Yerba Buena Level, Salon 7/8/9
9:00 AM - PP3.01
Neat and Complete: Thiolate-Ligand Exchange on a Silver Molecular Nanoparticle
Lina Abdul Halim 1 Osman M Bakr 2 Amala Dass 3 Nuwan Kothalawala 3
1King Abdullah University of Science and Technology Jeddah Saudi Arabia2King Abdullah University of Science and Technology (KAUST) Thuwal Saudi Arabia3University of Mississippi Oxford United StatesShow Abstract
Atomically precise thiolate-protected noble metal molecular nanoparticles are a promising class of model nanomaterials for catalysis, optoelectronics, and the bottom-up assembly of true molecular crystals. However, these applications have not fully materialized due to a lack of ligand exchange strategies that add functionality, but preserve the properties of these remarkable particles. In this presentation, we describe a method for the rapid (<30 s) and complete thiolate-for-thiolate exchange of the highly-sought-after silver molecular nanoparticle [Ag44(SR)30]-4.We discuss the mechanism behind this rapid exchange that allowed us to preserve the precise nature of the particles, and simultaneously replace the native ligands with ligands containing a variety of functional groups. We also show how we were able to process the particles into smooth thin films, paving the way for their integration into solution-processed devices.
9:00 AM - PP3.02
Ferroelectric Photovoltaic Effect in La and Ta Co-Doped BiFeO3 Thin Films
Rajesh K. Katiyar 2 1 Yogesh Sharma 2 Danilo Barrionuevo 2 1 Sudheendran Kooriyattil 2 1 Shojan Pavunny 2 Gerardo Morell 2 Brad R. Weiner 3 Ram S. Katiyar 2
1Institute of Functional Nanomaterials, University of Puerto Rico San Juan United States2Department of Physics, University of Puerto Rico San Juan United States3Department of Chemistry, University of Puerto Rico San Juan United StatesShow Abstract
Recently, observation of switchable polarization-induced ferroelectric photovoltaic effect (FEPV) in BiFeO3 (BFO) has attracted great interest. In order to improve its FEPV properties, co-substituted [Bi0.9La0.1][Fi0.97Ta0.03]O3 (BLFTO) films were fabricated on Pt/TiO2/SiO2/Si substrates by pulsed laser deposition (PLD). The phase formation of the films was confirmed by X-ray diffraction, Raman spectroscopy, XPS studies. The FEPV properties in La and Ta co-doped BiFeO3 (BFO) thin films were evaluated under illumination using sandwich configuration with ZnO:Al transparent conducting oxide (TCO) as top electrode. The TCO electrode was deposited by PLD using a shadow mask of 200 µm diameter. The band gap of the films was determined as 2.66 eV from spectrophotometric measurements, which is very close to that of pure BFO (2.7 eV). The ferroelectric nature of the films was characterized by P-E loop measurements, which indicated that leakage was still the prominent factor for not getting good polarization hysteresis. The piezo-force microscopy (PFM) studies however confirmed the ferroelectric nature of films. The open circuit voltage and short circuit current density were observed to be ~0.25 V and ~1.4 mA/cm2, respectivly. The photovoltaic effect of the films was studied as a function of distance between the electrodes in the planar configuration. The photovoltaic effect decreased with increase in separation between electrodes. We will present aforementioned properties and will discuss the intended photovoltaic application of this non linear dielectric material in details.
9:00 AM - PP3.04
A DNA-Hosted Gold Nanocluster Enhances Enzymatic Electroreduction of Oxygen by Mediating Efficient Electron Transfer
Saumen Chakraborty 1 Sofia Babanova 2 Reginaldo Rocha 1 Anil Desireddy 1 Kateryna Artyushkova 2 Plamen Atanassov 2 Jennifer Martinez 1
1Los Alamos National Laboratory Los Alamos United States2University of New Mexico Albuquerque United StatesShow Abstract
Few atom fluorescent noble metal nanoclusters (<2nm in diameter) hold the promise for a variety of groundbreaking applications across many disciplines of science including optoelectronic devices, biocompatible probes for cellular imaging, and catalysis. The size-dependent optical and electronic properties of these nanoclusters make them attractive materials to study. Here we report the synthesis and characterization of DNA-templated fluorescent gold nanoclusters (AuNCs) with potential applications as biocompatible probes for cellular imaging and mediators of electron transfer for oxygen reduction reaction (ORR). Our initial characterization shows that these AuNCs are formed by few Au atoms ligated to one DNA molecule, and display a large Stokes shift of ~200 nm (lambda;ex=430 nm, lambda;em=630 nm) with a multicomponent lifetime in the range of ~0.4-4 mu;s. TEM images show that these clusters are sub-nm in size (<1 nm). The presence of both a Au(0) core, and a Au(I) surface is observed from XPS studies of these AuNCs, suggesting that these materials are truly cluster in nature. Changes in nitrogen speciation in the AuNC sample compared to the parent DNA hints that the nitrogen atoms of nucleobases ligate the NCs. Treatment of these AuNCs with a strong reductant results in a loss of the luminescence properties suggesting that the primary source of luminescence is the surface Au(I) atoms. Applications of these AuNCs as targeted fluorescent probes for cellular imaging and as electrocatalysts for the ORR are currently being investigated.
9:00 AM - PP3.05
Effect of Substrate Topography on Grain and Pore Morphology Evolution in Nanoporous Gold Thin Films
Christopher Chapman 1 Pallavi Daggumati 2 Shannon C Gott 3 Masa Rao 3 4 5 Erkin Seker 2
1University of California, Davis Davis United States2University of California, Davis Davis United States3University of California, Riverside Riverside United States4University of California, Riverside Davis United States5University of California, Riverside Riverside United StatesShow Abstract
Nanoporous gold (np-Au) thin films, often produced by selective removal of silver from a gold-silver alloy, offer high electrical conductivity, catalytic activity, tunable pore morphology, and compatibility with conventional micropatterning techniques. These are critical properties for a number of important applications such as biosensors, fuel cells, and biomedical device coatings. In such applications, thin film coatings typically are applied on substrates with micro- to nano-scale features. As the precise control of pore morphology is essential for related applications, it is necessary to systematically investigate the effect of underlying substrate topography on np-Au thin films. In this study, we demonstrate a novel device architecture combing silicon surface patterns and sputter-coated np-Au films. Groove-based silicon gratings with groove widths varying between 150 nm to 50 µm were fabricated by photolithographic patterning, followed by pattern transfer to the underlying Si substrate by fluorine-based dry etching process. The micromachined silicon devices had an average ridge depth of 1.2 µm for gratings with groove widths above 500 nm, as confirmed by stylus-based profilometry. A 600 nm-thick gold-silver alloy film, as the precursor to the np-Au, was co-sputtered on the textured silicon chip. Grain size and distribution analysis by scanning electron microscopy coupled with digital image processing revealed that average grain size increased with increasing grating width. Subsequently, np-Au films with average pore size of 50 nm were obtained by dealloying the sputtered gold-silver film in nitric acid at 55°C. Dealloying step did not have a significant effect on pore moprhology as a function of grating width. Rapid thermal annealing was subsequently used to modify the pore morphology, in which heat facilitates surface diffusion of gold atoms leading to ligament and pore coarsening, which are hypothesized to be prone to mechanical constraints. Thermal treatment resulted in an increase in pore size for grating widths greater than 1 µm and preferential expansion of voids over pores in sub-micron gratings. In addition, the number of voids per unit area increased as the grating width decreased. In this study, we discuss the effect of surface topography on grain and pore morphology evolution as a function of thermo-mechanical constraints. The results include geometric, morphological, and elemental analysis of nanoporous gold films on the silicon substrate and the effect of thermal annealing at temperatures ranging from 200°C to 400°C. We expect these studies to provide insight into the nanostructured thin metal film behavior on textured substrates and facilitate cell-material interaction studies across nano- to micro-scale feature sizes.
9:00 AM - PP3.06
Electrocatalytic Oxygen Reduction Reaction Based on Atomically Precise Gold Nanoclusters
Woojun Choi 1 Kyuju Kwak 1 Dongil Lee 1
1Yonsei University Seoul Korea (the Republic of)Show Abstract
Oxygen reduction reaction (ORR) based on Pt metal catalysts is most generally used in fuel cells. However, although their high activity, Pt metal based ORR has fundamental limitation due to its high cost and limited abundance. For these reasons, non-Pt catalysts such as other noble metallic (eg., Au, Ag), bimetallic (eg., Au-Co, Pd-Co), non metallic (eg., carbon nanotube) catalysts based ORR are also widely studied. However the catalytic activity and durability of the non-Pt catalysts remain unsatisfactory and thus the development of Pt-free catalytic ORR is considered as promising research area. In this poster, we compared the ORR activities for a variety of sized gold nanoparticles protected with hexanethiol (C6S) ligands such as Au25(C6S)18, Au38(C6S)24, Au67(C6S)35, Au102(C6S)44, Au144(C6S)60, and Au333(C6S)79 by cyclic voltammetry (CV) and rotating disk electrode (RDE) techniques in basic media (0.1 M KOH). These well defined Au nanoparticels showed similarities and differences for their onset potentials, reduction currents, and number of electrons involved in the ORR. These size effects offer possibility to design new Pt-free ORR catalysts. Also we examined the catalytic activity of the Au nanoparticles immobilized in a sol-gel matrix that exhibited interesting activity for the oxygen electroreduction.
9:00 AM - PP3.07
Sensitivity Enhancement of Graphene-Coupled SPR Sensor Chip Using Layer-by-Layer Self-Assembly
Kyungwha Chung 1 Adila Rani 1 Dong Ha Kim 1
1Ewha Womans University Seoul Korea (the Republic of)Show Abstract
Graphene and its derivatives have been investigated extensively during the last decade because of their excellent thermal, mechanical and electric properties. Graphene also possesses very unique optical properties due to the linear dispersion relation and Dirac fermions which act as massless particles. Thus unique graphene plasmons can interact effectively with the incident photons. However, even though 2.3% of light absorption of single layer graphene is relatively high, it is required to enhance the light-matter interaction for the actual applications.1 In this regard, the use of graphene in conventional plasmonic devices has been suggested.
SPR-based sensors are versatile research tools for molecular biology. It is highly sensitive to the refractive index (RI) of the medium and binding events (analyte-receptor) cause the change in RI resulting in the SPR angle shift enabling label-free sensing. Many efforts were carried out to overcome the limit such as difficulty in detection of small analytes and insufficient sensitivity (nanomolar detection) compared to ELISA. Incorporation of plasmonic nanomaterials is one of the most exploited strategies in label-free format.2 Plasmonic nanomaterial-based SPR coupling induces the sensitivity by amplifying electromagnetic field.
In this work, graphene oxide (GO) and reduced graphene oxide (rGO) were introduced in SPR sensor chip in order to examine the coupling effect between graphene plasmons and propagating surface plasmons in Au film. Systematic and comparative studies on the deposition number and reduction of GO were conducted for the first time. Kretschmann configuration-based SPR sensor chip is composed of high refractive index glass prism and 48~50 nm of gold thin film. GO and rGO films were deposited on Au films by layer-by-layer self-assembly method and their RI sensitivity was compared in SPR-based sensors. Previous works revealed that graphene and its derivatives can enhance the sensitivity by increasing the attachment of biomolecules due to large surface area and by increasing electromagnetic field. By carrying out the bulk RI sensing, electromagnetic contribution of GO and rGO can be deconvoluted. The GO and rGO-deposited Au films showed different aspects in RI sensitivity: GO-Au film showed maximum sensitivity when the number of deposition was three while the RI sensitivity of rGO samples decreased with increasing number of layers. The biosensing activity was also performed with mass sensitivity of 1.43 ng mm-2. Deposition of GO and rGO didn't hinder "figure of merit" of sensor chip which is common in plasmonic nanostructure-deposited Au film while the sensitivity was enhanced compared to neat Au film.
1. Grigorenko AN, Polini M, Novoselov KS. Graphene plasmonics.Nat Photon 2012, 6:749-758.
2. Zeng S, Baillargeat D, Ho HP, Yong KT. Nanomaterials enhanced surface plasmon resonance for biological and chemical sensing applications.Chem Soc Rev 2014, 43:3426-3452.
9:00 AM - PP3.08
Bimetallic Nanoparticles with Controlled Compositions Supported on Organofunctionalized Mesoporous Silica: Relation Between the Composition and the Catalytic Activity
Joao Paulo Vita Damasceno 1 Camila Marchetti Maroneze 1 Mathias Strauss 2 Italo Odone Mazali 1
1Institute of Chemistry - State University of Campinas Campinas Brazil2Brazilian Nanotechnology National Laboratory (LNNano) Campinas BrazilShow Abstract
Several studies have been carried out in the last years aiming to a better and comprehensive understanding of structure-properties relationships of noble metal nanoparticles. In order to improve the knowledge about these relations, this work reports the surface modification of SBA-15 with an imidazolium ionic liquid-based alkoxysilane and its subsequent application in the synthesis of supported monometallic and bimetallic nanoparticles. The anion-exchange ability of the functionalized material was explored to promote the adsorption of Au and Pd anionic complexes on the porous framework, subsequently converted into metallic nanoparticles through the chemical reduction with NaBH4. The catalytic activity of the resulting materials were tested in the reduction of 4-nitrophenol to 4-aminophenol in aqueous solution. The structural characterization of the catalysts were carried out by SAXS and nitrogen adsorption-desorption isotherms, which confirmed the ordered porous structure of SBA-15, with average pore diameter of 8 nm and specific surface area (BET) equal to 800 m2 g-1. No obstruction or blockage of the porous structure was observed after the functionalization and the synthesis of the supported nanoparticles. Elemental analysis demonstrated that the functionalization degree was 0.65 mmol g-1. ICP-OES was carried out to quantify the weight percent of the loaded metals in the samples, which varied from 0.3 to 1.7 wt %. XRD and XPS were employed to estimate the crystallites sizes and to evaluate the formation of homogeneous or segregated phases. TEM images enabled the observation of the dispersion degree of the metallic nanoparticles through the silica support and showed that the pores acted as a template that controls the size of the nanostructures as well as a stabilizer that avoid the particles growth. The catalytic tests showed that the catalysts composed by Au0.2Pd0.8 and by Aushy;0.4Pd0.6 were more active than the samples containing only one metal.
9:00 AM - PP3.09
Thin Nanocomposites Films Using Polyaniline, Montmorillonite Clay and Gold Nanoparticles for Sensors Applications
Anerise De Barros 1 Carlos Jose Leopoldo Constantino 3 Mariselma Ferreira 2 Nilson Cristino da Cruz 1 Marystela Ferreira 4
1Paulista State University/UNESP Sorocaba Brazil2Univ Federal do ABC Sao Paulo SP Brazil3Paulista State University/UNESP Presidente Prudente Brazil4Satilde;o Carlos Federal University Sorocaba BrazilShow Abstract
During the past decade there has been a significant progress in the synthesis and characterization of nanocomposites, which can have unique properties due to the effect of the size of nanoparticles dispersed in a inorganic materials, such as clays and a polymeric matrix. Within this context, conducting polymers (CP) and montmorillonite clays are quite interesting materials in obtaining synergistic effects due to their relatively high electrical conductivity, chemical stability and low cost. For example, CP have been extensively employing to improve selectivity of modified electrodes in electrochemical sensor technology and act as an immobilizing matrix reducing interfering molecules. On the other hand, the use of gold nanoparticles (AuNPs) can increase the catalytic activity of sensors having modified electrodes, due to greater diffusion of electrons in the process. Here, nanocomposites formed from polyaniline (PAni), montmorillonite clay (MMTO) and gold nanoparticles (AuNPs) were obtained by the Langmuir-Blodgett (LB) technique, being characterized by UV-vis spectroscopy at each adsorbed bilayer. Results showed a good adsorption in the multilayer nanostructure formed, enabling the identification of PAni characteristic bands at ~ 300 nm (π-π* transitions) and at approximately 800 nm, attributed to the formation of a polaronic band corresponding to the doped state of PAni (electron delocalization due to the conjugation formed in the polymeric backbone). The Raman and FTIR spectroscopy confirmed the presence of both materials and the good influence of AuNPs in PAni properties. The DRX results showed indicated the influence of AuNPs for intercalation of PAni in interlamelar space of clay sheets. The other hand, it was possible to verify that the conductivity of PAni was not affect by the presence of AuNPs. It was possible to identify the oxidation peaks of PAni at 0.2 to 0.5 V from electrochemical measurements acquired for the MMTO/AuNPs/PAni LB films soaked in an HCl 0.1 mol.L-1 electrolyte solution, assigned respectively to the doped and undoped states of PAni by chloride ion. The sensor activity was evaluated by electrochemical measurements, being promising for application in environmental control for the detection of heavy metals, such as copper, lead and cadmium. These metals could be identified by standard potentials in approximately -0.04V for copper, -0.4V for lead and -0.7V for cadmium vs saturated calomel reference electrode (SCE).
9:00 AM - PP3.10
Hollow Nanocubes Made of Ag-Au Alloys for SERS Detection with Sensitivity of 10-8 M for Melamine
Jumei Li 1 Yin Yang 1 Dong Qin 1
1Georgia Institute of Technology Atlanta United StatesShow Abstract
In this work, we transformed Ag nanocubes into Ag-Au hollow nanocubes with a continuous shell of Ag-Au alloy on the surface and some remaining pure Ag in the interior. Upon removal of the pure Ag inside Ag-Au hollow nanocubes with aqueous H2O2, we obtained Ag-Au nanoboxes. We then systematically evaluated the SERS properties of the hollow nanocubes and nanoboxes by benchmarking against the Ag nanocubes. In one study, we collected the SERS spectra of 1,4-benzenedithiol (1,4-BDT) adsorbed on the surfaces of the nanoparticles when the samples were prepared using 1,4-BDT solutions with different concentrations. Our results showed that both the hollow nanocubes and nanoboxes exhibited much stronger SERS activity than the original Ag nanocubes. In particular, the remaining pure Ag inside the hollow nanocubes made a significant contribution to achieve SERS detection with sensitivity of 10-11 M for 1,4-BDT. We further demonstrated their capability for SERS detection of melamine at 10-8 M—a concentration much lower than the tolerance level of 1 ppm in infant formula. Additionally, we showed that the hollow nanocubes or nanoboxes with Ag-Au alloy shells on the surfaces were more stable than Ag nanocubes in an oxidative environment such as a solution containing an oxidant and/or halide ions. Taken together, these Ag-Au alloy nanostructures are good candidates for trace detection of biological and chemical analytes by SERS.
9:00 AM - PP3.11
Low-Temperature Modification of of Nanoporous Gold Morphology via Electro-Annealing
Tatiana Dorofeeva 1 Erkin Seker 1
1University of California Davis Davis United StatesShow Abstract
Nanoporous gold (np-Au) is an emerging material that has generated significant interest in the recent years due to its unique properties such a high electrical and thermal conductivity, high surface area-to-volume ratio, tunable pore morphology, and compatibility with microfabrication. These features made np-Au a popular material for fuel cells, biosensors, neural electrode coatings, and as a model system for studying nano-scale mechanics. Np-Au is produced by selective dissolution of silver from a gold/silver alloy, by a process known as dealloying, as gold atoms rearrange to create an open-pore morphology. Thermal treatment of the resulting np-Au structure increases surface diffusion of gold atoms and leads to coarser morphologies as a function of temperature and treatment duration. The extent of coarsening plays an essential role in the overall device operation and therefore precise control of morphology is necessary for attaining optimal device performance. Traditionally, thermal treatment in furnaces is used to obtain coarser morphologies, but this approach lacks the ability to create different morphologies on a single substrate. The ability to display multiple pore morphologies on a single substrate would greatly facilitate the identification of optimal morphologies that may enhance catalytic activity or surface-enhanced Raman signal from the metallic surface. Here, we present a novel technique based on electro-annealing to address this challenge and demonstrate several distinct morphologies on a single substrate. This technique is based on the principle that electrical current flowing in thin film traces lead to localized changes in current density as a function of trace geometry. At regions with smaller cross-section, increased current density leads to localized Joule heating. Electrical conductivity of np-Au thin films combined with rationally-designed trace geometries, allows for creating multiple and distinct pore morphologies via a short (less than 2 minutes), single treatment step performed at much lower (<150 #730;C) temperatures than those required for traditional thermal annealing (>250 #730;C). It is hypothesized that the reduced process temperature is achieved by electrically-assisted phenomena that contribute to thermally-assisted surface diffusion of gold atoms responsible for coarsening. Annealing at lower temperatures opens the door to the use of substrates with lower melting temperatures, such as many plastics. Overall, this approach can be easily scaled up to display multiple pore morphologies on a chip and should facilitate the production of high-throughput screening platforms on various substrates for studying structure-property relationships and identifying optimal morphologies for desired applications.
9:00 AM - PP3.12
Synthesis and Properties of Multifunctional Nanocomposte Au-YSZ Thin Films
David Horwat 1
1Institut Jean Lamour-Universiteacute; de Lorraine Nancy FranceShow Abstract
The gold/yttria-stabilized zirconia (Auminus;YSZ) nanocomposite system is a particularly interesting candidate for multifunctional applications. First, oxide-supported gold nanoparticles are very promising to dramatically lower the inset temperature of several catalytic reactions to room temperature or close to room temperature.1 This approach currently stimulates many studies in the field of heterogeneous catalysis. Second, gold nanoparticles on different supports and gold/oxide nanocomposite films exhibit localized surface plasmon resonance (LSPR) in the visible range, making it useful for applications as a chemical sensing layer2 and in the emerging field of plasmonics. Effectively, it enables combining the specific properties of YSZ, such as oxide ion conductivity, to the LSPR and catalytic activity provided by the gold nanoparticles. Third, as long as the gold loading is sufficient, annealing such films in air induces the relocation at the surface of some of the gold atoms to form a soft layer with adaptive tribological properties.3
This communication presents reactive magnetron co-sputtering syntehsis of Au-YSZ thin films, their optical, electrical,4 catalytic5 and frictional properties6 in connection to their microstructure and local chemistry. It is shown that:
- Thermally resilient LSPR can be achieved
- The electrical conductivity can be tuned by controlling the gold content, thermal annealing or laser interferrence patterning
- The produced layers can act can electrochemically promote the oxidation of methanol
- Drastic reduction of the friction coefficient can be obtained in as-deposited films, compared to pure YSZ, and further lowered using Laser interferrence patterning
1 Gold Bull. 37 (2004) 3minus;11
2 J. Phys. Chem. C 115 (2011) 6283minus;6289
3 Surf. Coat. Technol. 146minus;147 (2001) 351minus;356
5 ACS Appl. Mater.nter. 6 (2014) 13707-13715
6 J. Catal. 317 (2014) 293-302
7 J. Mater. Res. 27 (2012) 879-885
9:00 AM - PP3.13
Magnetic-Plasmonic Fe2O3/Au Hybrid Nanostructures for Biomedical Applications
Hanene Belkahla 1 2 Tijani Gharbi 1 Guillaume Herlem 1 Souad Ammar 2 Walid Dachraoui 3 Damien Alloyeau 3
1University of Franche Comte Besanccedil;on France2University of Paris Diderot Paris France3University of Paris Diderot Paris FranceShow Abstract
Iron oxide nanoparticles (NPs) have become increasingly important for cutting-edge applications in biomedicine due to both their biocompatibility and attractive magnetic properties. Super-paramagnetic magnetite nanocrystals possess high magnetic susceptibility, low remanence, low coercivity, and high saturation magnetization, making them ideal candidates for various biomedical applications including magnetic resonance imaging (MRI), magnetically controlled drug delivery and magnetic hyperthermia . Manipulation of these NPs for in-vivo diagnostic and/or therapy assays requires their coupling through covalent bounding to bioactive molecules (antibodies, enzymes, proteins, DNAhellip;). This could be greatly simplified by coating these probes by a gold nanoshell which exhibits both high biocompatibility and affinity for binding to amine/thiol terminal groups of biorganic molecules .
Here, we report different facile and highly reproductive synthetic processes enabling the coating of polyol-made about 10 nm sized iron oxide NPs by a more or less continuous gold shell. The main strategy consists of grafting at the surface of these NPs charged molecules, namely positively charged (3-aminopropyl)triethoxysilane (APTES) and negatively charged citric acid, using sol-gel chemistry and surface complexation, respectively. These surface charges attract oppositely charged preformed gold particles or dissolved gold cations. In the first case discrete gold nanodots may be attached at the surface of the magnetic NPs, while in the second case, a continuous nanoshell may be produced around them. In all the cases, the morphological, optical and magnetic properties of the resulting hetero-nanostructures were investigated and described in relation with the quantity of deposited gold.
9:00 AM - PP3.14
Nanoporous Gold Thin Films with TiO2 for H2 Oxidaion
Thi Phuong Quynh Bui 1 Kamran Qadir 2 Jeong Young Park 2 Sang Hoon Kim 1
1Korea Institute of Science and Technology Seoul Korea (the Republic of)2KAIST Daejeon Korea (the Republic of)Show Abstract
Nanoporous Gold (NPG) is a novel three dimensional, bicontinous and interconnected nanostructured monolithic material which serves as promising platform to design tailored catalysts via controlled surface modification through oxide deposition such as TiO2. In this presentation, we will show that the catalytic activity of our NPG films (~150 nm thick) for H2 oxidation is enhanced by depositing TiO2 on them. We fabricated NPG films of varying porosity by de-alloying Si from AuxSi1-x alloy of varying Au/Si compositions. Our NPG films were further modified by titania deposition on the NPG films via titanium isopropoxide (TTIP) impregnation. In order to engineer catalytically active perimeter interface at the TiO2/NPG junction, concentration of TTIP precursor was varied (up to 1 wt%) in liquid phase deposition. We found enhancement of H2 oxidation activity for inverse TiO2/NPG catalysts while pure NPG exhibited low turnover frequency (TOF). TOF increased as the weight fraction of TTIP was increased to 0.5 wt%. It however decreased for higher than 0.5 wt% TTIP, suggesting reduction of perimeter interface area between TiO2 and NPG body, which serves as active sites.
9:00 AM - PP3.15
The Interaction of Gold Nanoparticles with a Range of Cationic and Anionic Dyes
Hazel Kitching 1 Anthony J Kenyon 1 Ivan Parkin 2
1University College London London United Kingdom2University College London London United KingdomShow Abstract
The growing epidemic of antibiotic-resistant infections, combined with a decrease in the research and production of new antibiotics, continues to plague global healthcare systems.1 There is a pressing need to develop alternative treatments for common drug-resistant bacteria for when standard antibiotic therapy fails. One such treatment is photodynamic therapy (PDT), which uses photosensitizers to kill bacteria or somatic cells through the production of cytotoxic singlet oxygen.2 Previous research has shown that combining photosensitizers with nanomaterials,3, 4 including gold nanoparticles,5 greatly enhances their cytotoxic efficacy; however the mechanisms at work are poorly understood.
In this work a range of dyes, including some known photosensitizers, were introduced to a solution of gold nanoparticles synthesised via the citrate-reduction method. It was found that the nanoparticles interacted strongly with cationic dyes and in some cases enhanced absorption was observed during UV-visible spectroscopy (UV-Vis) observation of titration experiments. We also show that the addition of cationic dyes to gold nanoparticles triggers aggregation of the nanoparticles into large clusters up to several micrometres across. Nanoparticles were seen to fragment and agglomerate at high concentrations of cationic dye in the solution. None of these effects were observed when the nanoparticles were titrated with anionic dyes, nor when silver nanoparticles synthesised by the same method were titrated with either cationic or anionic dyes.
The three cationic dyes which showed enhanced absorption during UV-Vis - acridine orange, toluidine blue and crystal violet - are known photosensitizers. The phenomenon of enhanced absorption has been reported previously for toluidine blue and was shown to be accompanied by a marked increase in cytotoxicity.5, 6 It has not been previously reported for crystal violet and acridine orange, however, and singlet-oxygen generation measurements are planned to deduce the antimicrobial capabilities of these new conjugations.
1. B. Spellberg, R. Guidos, D. Gilbert, J. Bradley, H. W. Boucher, W. M. Scheld, J. G. Bartlett, J. Edwards and t. I. D. S. o. America, Clinical Infectious Diseases, 2008, 46, 155-164.
2. T. J. Dougherty, C. J. Gomer, B. W. Henderson, G. Jori, D. Kessel, M. Korbelik, J. Moan and Q. Peng, Journal of the National Cancer Institute, 1998, 90, 889-905.
3. A. C. Khazraji, S. Hotchandani, S. Das and P. V. Kamat, The Journal of Physical Chemistry B, 1999, 103, 4693-4700.
4. A. Khdair, B. Gerard, H. Handa, G. Mao, M. P. V. Shekhar and J. Panyam, Molecular Pharmaceutics, 2008, 5, 795-807.
5. S. T. Naima Narband, Ivan P. Parkin, Jesuacute;s Gil-Tomás, Derren Ready, Sean P. Nair and Michael Wilson, Current Nanoscience, 2008, 4, 409-414.
6. N. Narband, M. Uppal, C. W. Dunnill, G. Hyett, M. Wilson and I. P. Parkin, Physical Chemistry Chemical Physics, 2009, 11, 10513-10518.
9:00 AM - PP3.16
Photocatalytic and Electrocatalytic Activities of Metal Nanoparticle/ZnO Composites
YongJin Lee 1 HyunJi Kim 1
1Yonsei Univ Seoul Korea (the Republic of)Show Abstract
This poster presents photocatalytic and electrocatalytic activities of noble metal nanoparticles (metal = Au, Ag, Pd, and Pt) anchored on the surface of ZnO nanoparticles. The ZnO-metal composites were prepared by anchoring glutathione-protected metal nanoparticles on ZnO surface and photocatalytic experiments were conducted with composite colloids under light (> 320 nm) in a deaerated 1:1 (v/v) EtOH-H2O medium. The photocatalytic activity of bare ZnO for the reduction of azobenzene was found to be negligible, but it increased dramatically upon coating of metal nanoparticles. The enhancement was highest with Pd nanoparticles, followed by Pt, Au and Ag. Similar metal effect has been observed in the electrocatalytic reduction of azobenzene. Through product analysis of the photocatalytic reactions, it was found that azobenzene was reduced to hydrazobenzene via proton-coupled electron transfer reaction. The metal effect can be explained by the proton binding tendency of metals in the composites that controls the proton-coupled electron transfer reaction. Reduction of carbon dioxide which is considered as another proton-coupled electron transfer reaction is also discussed.
9:00 AM - PP3.17
A New Route for Synthesis of Au Nanoparticle Clusters by Using Galvanic Replacement of Ag Nanoparticles and Their Efficient Surface-Enhanced Raman Scattering Platforms
Seunghoon Lee 1 Sang Woo Han 1
1KAIST DaeJeon Korea (the Republic of)Show Abstract
Compared with individual Au nanoparticle, Au nanoparticle clusters (AuNPCs) show efficient surface-enhanced Raman scattering (SERS) performance because they are rich in interparticle gaps, which can act as hot spots for strong electromagnetic field enhancement. Moreover, AuNPCs are very stable SERS platforms for biosensing applications. However, the lack of simple and reliable methods for preparing AuNPCs with well-defined structural parameters is a major obstacle for exploiting the unique plasmonic properties of AuNPCs toward practical applications. In practice, we applied AuNPCs on organic photovoltaic solar cell, and they show the high performance power conversion efficiency for the single active layer organic photovoltaics.1
In the present work, we present a facile aqueous synthetic method for the preparation of AuNPCs by the controlled galvanic replacement of Ag nanoparticles with Au precursors. The final morphology of AuNPCs could readily be tuned by changing the structure of Ag nanoparticles. The prepared AuNPCs showed single-molecule level SERS detection and stability for various analytes both in water and under physiological conditions. We expect that the present study will provide a new direction for the development of an efficient plasmonic platform for biosensing and imaging and that it can also be applied to the fabrication of intriguing nanoarchitectures with desirable morphologies and functions.
1. H. I. Park, S. Lee, J. M. Lee, S. A. Nam, T. Jeon, S. W. Han, S. O. Kim, High Performance Organic Photovoltaics with Plasmonic-Coupled Metal Nanoparticle Clusters. ACS Nano in press.
9:00 AM - PP3.18
Interaction of Ligand-Capped Gold Nanoparticles with Two Dimensional Atomic Layered Nanomaterials
Serena Low 1 Sydney Gang 1 Young-Seok Shon 1
1California State University, Long Beach Long Beach United StatesShow Abstract
Two dimensional (2D) atomic layered nanomaterials exhibit some of the most striking phenomena in modern materials research and hold promise for a wide range of applications including energy and device technology. More recently, graphene oxide-metal nanoparticle hybrid materials have been of increasing interest due to their potential applications in biological and environmental industries. Our research specifically targets the preparation of gold nanoparticle catalysts supported on 2D nanomaterials, including graphene oxide and bismuth selenide nanosheets, using the strategy of pre-formed nanoparticle self-assembly. This strategy is especially useful for fine tuning the size and monodispersity of gold nanoparticles that have a direct influence over the catalytic activity of the hybrid materials. Ultimately, the use of aforementioned 2D supports, having extremely high surface area to volume ratio, excellent electric conductivity, and unique characteristics of enhancing mass transport of reactants to catalysts, would maximize the activity of surface-assembled metal nanoparticle catalysts. As an initial step, the current research aims at understanding the interaction between ligand-capped gold nanoparticles and graphene oxide/bismuth selenide nanosheets. For this task, hydrophobic and hydrophilic ligand-capped gold nanoparticles with different core sizes are synthesized and mixed with 2D supports (graphene oxide or bismuth selenide nanosheets). By varying the functional groups on the ligands between alkyl, aromatic, amine and alcohol groups, we are able to induce different interactions such as Van der Waals, π-π stacking, dipole-dipole, and hydrogen bonding. The solvent and concentration effects on the interactions between 2D supports and nanoparticles are also tested. The adsorption of gold nanoparticles on to the surface of 2D supports was monitored using UV-vis spectroscopy and transmission electron microscopy (TEM). The results show that amine-functionalized hydrophobic ligand-capped gold nanoparticles produce well dispersed nanoparticles on the surface of graphene oxide without the formation of locally aggregated particle domains. The same nanoparticles are also found to have a strong interaction with bismuth selenide nanosheets forming gold nanoparticle-bismuth selenide hybrid nanostructures. Once the gold nanoparticles are anchored onto the 2D materials, the surface ligands are partially removed by annealing the nanoparticles at higher temperature, which enable the nanoparticles to act as supported catalysts. Future work will include understanding the catalytic behaviors of the produced hybrid nanomaterials for model organic reactions (e.g. oxidation of benzyl alcohol).
9:00 AM - PP3.19
Seed-Mediated Growth of Gold Nanocrystals: Changes to the Crystallinity or Morphology as Induced by the Treatment of Seeds with a Sulfur Species
Yiqun Zheng 3 Ming Luo 1 Younan Xia 2
1Georgia institute of Technology Atlanta United States2Georgia Institute of Technology Atlanta United States3Georgia Institute of Technology Atlanta United StatesShow Abstract
This presentation reports our observation of changes to the crystallinity or morphology during seed-mediated growth of Au nanocrystals. When single-crystal Au seeds with a spherical or rod-like shape were treated with a chemical species such as S2O32- ions, twin defects were developed during the growth process to generate multiply twinned nanostructures. X-ray photoelectron spectroscopy analysis indicated that the S2O32- ions were chemisorbed on the surfaces of the seeds during the treatment. The chemisorbed S2O32- ions somehow influenced the crystallization of Au atoms added onto the surface during a growth process, leading to the formation of twin defects. In contrast to the spherical and rod-like Au seeds, the single-crystal structure was retained to generate a concave morphology when single-crystal Au seeds with a cubic or octahedral shape were used for a similar treatment and then seed-mediated growth. The different outcomes are likely related to the difference in spatial distribution of S2O32- ions chemisorbed on the surface of a seed. This approach based on surface modification is potentially extendable to other noble metals for engineering the crystallinity and morphology of nanocrystals formed via seed-mediated growth.
9:00 AM - PP3.20
Stability of Hollow Gold Nanospheres and Gold Nanorods Functionalized with Mono-, Bi- and Tridentate Polyethylenglycolthiol Ligand
Julie Ruff 1 Ulrich Simon 1
1RWTH Aachen University Aachen GermanyShow Abstract
Hollow gold nanospheres (HAuNS) and gold nanorods (AuNR) are promising contrast agents for photoacoustic tomography due to their strong and tunable absorbance in the optical window of biological tissues between 600 and 900 nm. HAuNS are obtained via reduction of tetrachloro auric acid by sodium borohydride, in the presence of citrate as capping ligands, on cobalt nanoparticles as sacrificial templates. AuNR are obtained following a seed-mediated growth process. For increased stability and possible biocompatibility that allow in vivo applications of HAuNS and AuNR, PEGylation via a ligand exchange with PEG (polyethylene glycol) ligands bearing thiols as anchor groups (PEG thiols) needs to be performed. We report the synthesis and the stabilization by mono-, bi- and tridentate PEG thiols of HAuNS with 35 nm diameter, having a shell thickness of 5.3 nm and an absorbance maximum at 852 nm, as well as the synthesis of AuNR with a length of 60 nm, having a width of 17 nm and a longitudinal absorbance maximum at 761 nm. Therefore, novel bi- and tridentate PEG thiols were synthesized comprising methoxy end groups and having similar molecular weights of around 5000 Da. The stability of these PEGylated HAuNS and AuNR was explored in three different aspects: (1) stability towards competition reactions with the strong binding ligand dithiothreitol (DTT), (2) resistance towards oxidative Au dissolution with potassium cyanide, and (3) colloidal stability, tested by addition of salt. These studies revealed improved colloidal stability for all PEGylated HAuNS and AuNR compared to citrate or CTAB stabilized ones, respectively and an increasing stability with increasing number of thiol anchor groups. Findings about the reduced cytotoxicity after PEGylation of all species as well as no significant difference in the cytotoxicity between the mono-, bi- and tridentate PEGylated particles complete this work.
9:00 AM -
PP3.03 moved to PP4.05.5
Tuesday AM, April 07, 2015
Marriott Marquis, Yerba Buena Level, Salon 2/3
9:30 AM - *PP1.01
Total Structures of Atomically Precise Gold Nanoparticles and Beyond
Rongchao Jin 1
1Carnegie Mellon University Pittsburgh United StatesShow Abstract
Determining the total structures of nanoparticles constitutes a major goal in nanoscience research. Gold nanoparticles are particularly attractive due to their extraordinary stability and elegant optical properties. A prerequisite to total structure determination is to obtain atomically precise nanoparticles, which had been a major challenge in the past research and thus hampered the pursuit of fundamental science of nanoparticles. We have recently developed successful methodologies for synthesizing atomically precise gold nanoparticles protected by thiolates (denoted as Aun(SR)m, with n ranging from a few dozens to hundreds). Such ultrasmall nanoparticles (ca. 1-3 nm) exhibit distinct quantum size effects and interesting electronic/optical properties, which are fundamentally different from the plasmon-dominated properties of their larger counterparts (e.g. 5-100 nm nanoparticles). New types of atom-packing structures have been discovered in ultrasmall Aun(SR)m nanoparticles through X-ray crystallographic analysis. These well-defined nanoparticles hold potential in catalysis as new model catalysts, and atomic level structure-reactivity correlation will ultimately offer fundamental understanding on nanocatalysis.
10:00 AM - PP1.02
Unusual Non-Spherical Structures and Electronic Properties of Diphosphine-Protected Gold Clusters
Katsuaki Konishi 1
1Hokkaido University Sapporo JapanShow Abstract
Recently there have been considerable interests in the chemistry of atomically precise gold clusters with defined nuclearity and geometrical structures because they display molecular-like features that are virtually different from conventional colloidal nanoparticles. Phosphine-ligated gold clusters have a long history of studies to offer a library of diverse geometrical and electronic structures. X-ray crystal structures of monophosphine-ligated clusters have revealed that they generally favor to take icosahedron-based sphere-like geometries, but we recently found that the use of multidentate ligand sometimes allows the generation of exceptional non-spherical structures with anisotropic shapes. Here we show geometrical structures and electronic properties of such examples, which have nuclearity of 6, 7, 8 and 11. Unlike conventional sphere-like clusters such as icosahedral Au13, these anisotropic clusters all exhibit characteristic absorption band(s) in the visible region. The optical properties are strictly dependent on not only the nuclearity but also the cluster geometry. For some clusters bearing extra gold atoms attached to a polyhedral core (core+exo type), TD-DFT studies revealed that the exo gold atoms play a critical role in the emergence of unique electronic structure and distinctive optical features. We also report the syntheses of organic-functionalized cluster derivatives and their stimuli responsive functions.
ref) Struct. Bond., 2014, 161: 49-86; Angew. Chem. Int. Ed., 2011, 50, 7442; Chem. Commun., 2012, 48, 7559; Inorg. Chem., 2013, 52, 6570; J. Am. Chem. Soc., 2013, 135, 16078; J. Am. Chem. Soc., 2014, 136, 12892.
10:15 AM - *PP1.03
Ligand-Protected Gold Clusters with Novel Interfacial Structures
Tatsuya Tsukuda 1
1The University of Tokyo Tokyo JapanShow Abstract
We present two topics on development of new ligand-protected Au clusters by controlling the interfacial structures.
1. Protection of Gold Clusters by Bulky Thiolates
Bulky arenethiols, EindSH (Eind = 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl) and DppSH (Dpp = 2,6-diphenylphenyl), were used as protecting ligands with an aim to suppress the formation of -SR-[Au(I)-SR-]n oligomers on the Au core. Au41(SEind)12 and Au25(SDpp)11 were obtained by mixing of the hydrosol of small (diameter<2 nm) PVP-stabilized Au clusters and the toluene solution of the corresponding thiol and subsequent etching process. As expected, the ligand-to-Au ratios of Au41(SEind)12 and Au25(SDpp)11 are significantly smaller than those of Au:SR reported so far. Structural characterization of these isolated clusters suggests that the bulky thiolates are bonded directly to the surface of Au41 with twisted pyramidal motif and Au25 with vertex-shared bi-icosahedral motif.
2. Protection of Gold Clusters by Terminal Alkynes
Gold clusters protected by terminal alkynes, 1-octyne (OC-H), phenyl acetylene (PA-H) and 9-ethynyl-phenanthrene (EPT-H), were prepared by the ligand exchange of the small (diameter<2 nm) Au:PVP clusters. Vibrational spectroscopy revealed that the terminal hydrogen is lost during the ligand exchange. A series of precisely-defined gold clusters, Au34(PA)16, Au54(PA)26, Au30(EPT)13, Au35(EPT)18, and Au41-43(EPT)21-23, were synthesized and characterized in detail to obtain further insight into the interfacial structures. An upright configuration of the alkynes on Au clusters was suggested from the Au to alkyne ratios and photoluminescence from the excimer of the EPT ligands. EXAFS analysis implied that alkynyl carbon is bound to bridged or hollow sites on the Au cluster surface.
10:45 AM - PP1.04
Synchrotron-Based X-Ray Spectroscopy Studies of Atomically Precise Gold Nanoclusters: The Impact of Composition, Core Geometry and Metal-Ligand Interactions on Structure and Electronic Properties
Daniel M Chevrier 2 Chenjie Zeng 1 Xiangming Meng 4 Zhikun Wu 5 Mark A. MacDonald 2 Tang Qing 3 Amares Chatt 2 Manzhou Zhu 4 De-en Jiang 3 Rongchao Jin 1 Peng Zhang 2
1Carnegie Mellon University Pittsburgh United States2Dalhousie University Halifax Canada3University of California, Riverside Riverside United States4Anhui University Hefei China5Anhui Key Laboratory of Nanomaterials and Nanotechnology Hefei ChinaShow Abstract
Gold nanoclusters (Au NCs), containing only tens or hundreds of gold atoms, exhibit extraordinary optoelectronic and structural properties much different than the bulk and even larger gold nanoparticles . These ultrasmall gold nanoparticles are promising for next generation of sensor devices and catalysts. Due to the ultra-small size regime of Au NCs (~1-2 nm), it is often challenging to understand the origin of their unique properties which are highly sensitive to size and composition . Although recent advancements in Au NC synthesis have produced an extensive library of total structures from single-crystal X-ray diffraction characterization, a deeper understanding of Au NC local structure and electronic properties remains to be unlocked by probing metal and ligand environments via X-ray spectroscopy. Presented herein are recent synchrotron-based X-ray spectroscopy studies on the bonding properties of thiolate-protected gold nanoclusters (Aun(SR)m, SR-thiolate ligand) with varied composition (Au19(SR)13, Au24(SR)20 and Au25(SR)18) , a selenolate-protected surface (Au25(SeR)18)  and face centered cubic (FCC)-ordered core structures (Au28(SR)20, Au36(SR)24 and Au44(SR)28) [5,6]. As seen for Au19 and Au24, even a small change to the core composition or relative Au/SR ratio (compared to the Au25 model) drastically changes the structural and electronic properties . For both FCC-ordered core NCs and the selenolate-protected Au25 NC, an unexpected thermal contraction property was detected with temperature dependent X-ray absorption experiments [4-6]. FCC-ordered core structures contain tightly bonded Au4 units, important for rationalizing the thermal contraction of the metal core and the highly localized valence electronic structure. Selenolate-protected gold nanoclusters were found to have weak aurophilic interactions (compared to its thiolate-protected analogue, Au25(SR)18) on the surface that become stronger with increasing temperature, which potentially induce a contraction of the metal core. Furthermore, XAS and supporting theoretical calculations on site-specific ligand and metal environments offer a new and exciting perspective on the bonding properties gold nanoclusters.
 Jadzinsky et al. Science 2007, 318, 430minus;433.
 Qian et al. Acc. Chem. Res. 2012, 45, 1470minus;1479.
 Chevrier et al. J. Phys. Chem. C 2012, 116, 25137-25142
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 Chevrier et al. J. Phys. Chem. C 2014, submitted
 Chevrier et al. J. Phys. Chem. Lett. 2013, 4, 3186-3191
11:30 AM - *PP1.05
Molecular Silver-Gold Nanoparticle Alloys with Long Photoluminescence Lifetimes: Atomically Precise, Solution Processable Electron Donors
Osman M Bakr 1
1King Abdullah University of Science and Technology (KAUST) Thuwal Saudi ArabiaShow Abstract
Nanoparticles with their solution processability and size-tunable optical properties offer a wide range of opportunities for designing inexpensively fabricated photovoltaics and photocatalysts. On the other hand, even nominally monodisperse nanoparticles have a large degree of heterogeneity in the number of atoms of their core and ligands of their shell, which makes their properties difficult to model and predict. There is, however, a special class of homogeneous nanoparticles, known as molecular metal nanoparticles or atomically discrete nanoclusters, whose complete structure (core and shell) is exactly determinable and feasible to model. These precise materials have the potential to revolutionize the understanding of nanoparticle photovoltaics, catalysis, and charge transport properties. Unfortunately a) the number of reported molecular metal nanoparticles still remains modest; b) there are very few examples of such particles that are efficient in being both visible sensitizers and electron donors; and c) the particle&’s are usually synthesized with capping ligands and solvents that are unsuitable for the end application. Those are still major bottlenecks that have so far limited the utility of this promising class of nanomaterials.
In this presentation we reveal the total crystal structure and photophysical properties of a novel family of thiolate-protected molecular silver-gold nanoparticle alloys. Time-resolved photoluminescence and transient absorption spectroscopies were used to investigate the materials. The particles possess remarkably long photoluminescence lifetime (>150 ns), and have been found to be efficient electron donors when paired with small organic molecule acceptors. We show that with the right choice of ligands these particles can be used as efficient sensitizers for semiconductor systems utilized in the photocatalytic production of hydrogen. We discuss the role played by the ligand&’s structure and binding affinity to the metal, in determining the particle&’s size and promoting interfacial electron transfer.
The developments highlighted in this presentation pave the way for exploring practical applications of molecular noble metal nanoparticles as sensitizing donors in solution-processed photovoltaics and photocatalysts.
12:00 PM - PP1.06
Toward the Creation of Stable, Functionalized Metal Clusters
Yuichi Negishi 1
1Tokyo University of Science Tokyo JapanShow Abstract
Nanomaterials which exhibit both stability and functionality are currently considered to hold the most promise as components of nanotechnology devices. Thiolate (RS)-protected gold nanoclusters (Aun(SR)m) have attracted significant attention in this regard and, among these, the magic clusters are believed to be the best candidates since they are the most stable. Our group has attempted to establish methods of modifying magic Aun(SR)m clusters, with the goal of creating nanomaterials which are both robust and functional, by increasing the functionality of the clusters. As shown in many previous gas phase studies, doping small metal clusters with heteroatoms has a significant effect on their stability as well as their physical and chemical properties. It was therefore anticipated that the properties of magic Aun(SR)m clusters would also be significantly modified by doping with heteroatoms. In addition, protection of magic Aun(SR)m clusters by selenolate ligands and functionalized thiolates was considered to be useful approachs. Therefore, we have investigated the effects of heteroatom doping, protection by selenolate ligands and protection by functionalized thiolates on the stability and physical/chemical properties of these clusters. Our studies, therefore, have essentially been aimed at devising methods of tailoring magic Aun(SR)m clusters to produce compounds which are stable and exhibit useful properties. In this presentation, I report our studies towards this goal and the obtained results.
12:15 PM - *PP1.07
Chiral Ligand-Protected Bimetallic Nanoclusters: How Does the Metal Core Configuration Influence the Nanoclusterrsquo;s Chiroptical Responses?
Hiroshi Yao 1
1University of Hyogo Hyogo JapanShow Abstract
The desire to fabricate materials with well-defined, controllable physicochemical properties and structures on a nanoscale has generated considerable interest in bimetallic nanoclusters or nanoalloys. Interactions between the constituent atoms can modify the alloy&’s electronic structure and surface composition, leading to enhanced chemical, catalytic, and optical properties. In particular, the gold-based bimetallic system in very small (< ~2 nm) nanoclusters has received much attention, since the alloying or segregation (that is, bimetallic core configuration) can lead to significant perturbations on the electronic structure as well as its chemical/catalytic properties.
From a viewpoint of cluster chemistry, on the other hand, recent advances in the selective synthesis of atomically precise, thiolate-protected gold nanoclusters with molecular purity have motivated researchers to investigate their curious structures and physicochemical properties. In the nanosystems, it is now accepted that they are composed of a metal core surrounded by oligomeric -[S-Au]n-S- motifs often called “staples” or “semi-rings”. Therefore, the heteroatom doping (or alloying) in gold nanoclusters allows to probe the atomic sensitivity of the nanocluster&’s physical and chemical properties, as well as imparting the nanocluster with new properties.
The main objective in this study is to gain insight into the electronic structures and chiroptical responses of bimetallic Au-Pd and Au-Ag nanoclusters protected by chiral thiolate ligand, glutathione (GSH), and compare them with monometallic counterparts. The effect of Pd or Ag doping on the chiroptical responses of optically active Au nanoclusters as well as the importance of the bimetallic core configurations are discussed. Briefly, we find that GS-protected Au-Pd or Au-Ag nanoclusters exhibit quite different Cotton effects from those of the monometallic nanoclusters in metal-based electronic transition regions. In the Au-Pd system, all bimetallic nanoclusters exhibit featureless absorption profiles, but their circular dichroism (CD) signals were rather structured, offering a greater advantage in detecting a foreign atom doping in the nanocluster systems. In the Au-Ag system, interestingly, the nanocluster compounds exhibit weaker CD responses than those of the corresponding Au counterparts. The CD decrease can be explained in terms of the increased geometrical isomers that are formed by statistical distribution of Ag heteroatoms in the nanocluster, since an increased number of possible configurations is expected to give the average in the CD response with positive and negative bands of different optical isomers.
12:45 PM - PP1.08
Ligand Effect on Stability of Au24(SR)20 Cluster and Its Implication on the Structural Prediction of Au18(SR)14 Cluster
Qing Tang 1
1University of California, Riverside Riverside United StatesShow Abstract
Structure prediction is the greatest challenge in the computational studies of thiolate-protected gold nanoclusters. Usually a simple ligand such as a methyl group is used to replace complex ligands for efficiency in exploring the relative stability of different isomers. However, the isomer stability may depend on the ligand group, which is particularly important for the large protecting ligand wherein the vdWs interactions play a significant role. A case in point is the Au24(SR)20 nanocluster. Here we show that changing the R group of Au24(SR)20 from CH2CH2Ph to CH2Ph-tBu leads to different lowest-energy isomers. Thus the ligand plays a crucial role in dictating the isomer stablility. This insight prompts us to perform the structural search of Au18(SR)14 cluster with the consideraction of both the simplified -CH3 group and the real ligand (cyclo-hexane) used in experiment.
De-en Jiang, University of California, Riverside
Dongil Lee, Yonsei University
Yuichi Negishi, Tokyo University of Science
Jie Zheng, The University of Texas at Dallas
Symposium Support World Gold Council
Wednesday PM, April 08, 2015
Marriott Marquis, Yerba Buena Level, Salon 2/3
2:30 AM - PP5.01
Commercialising Gold-Based Technologies - Challenges and Opportunities in 2015
Trevor Keel 1
1World Gold Council London United KingdomShow Abstract
Gold, contrary to common belief, is a critically important industrial metal and is used widely in the electronics, chemical, medical and engineering sectors. In 2013, industrial demand for gold stood at ~400 tonnes, which represents ~10% of total demand across the entire market.
This paper will give a general overview of gold&’s place in technical applications in 2015, and will then focus on the challenges and opportunities in the development of new commercial uses, both from a scientific and non-scientific perspective. Specific examples of commercialisation efforts across a range sectors will be discussed, and the challenges experienced in some cases, particularly as a consequence of the wider gold market in recent years, will be highlighted. Finally, a brief review of the patent literature will be presented.
2:45 AM - *PP5.02
George C. Schatz 1
1Northwestern University Evanston United StatesShow Abstract
This talk will emphasize recent theory and experiments which have probed the effect of arrays of gold particles in 1D, 2D and 3D on optical response, with emphasis on the use of these array structures as metamaterials and in lasing applications. The arrays in 1D and 2D can be made using standard lithography tools, but much of the talk will emphasize bottom-up assembly of arrays that is possible using DNA-functionalized nanoparticles and self-assembly of nanoparticle superlattices driven by DNA hybridization. We show that the array structures lead to hybrid optical modes in which localized surface plasmon resonances in the nanoparticles are coupled with photonic modes of the lattices. These hybrid modes are often much narrower than the isolated particle plasmons, leading to greater field enhancements that are of interest in SERS, and greater refractive index sensitivity. In addition, we show that these modes make it possible to generate a new class of sub-wavelength lasers in which excitons in laser dyes are coupled with the hybrid lattice modes to produce enhanced stimulated emission. And finally we show new metamaterials properties in some of the lattices.
3:15 AM - PP5.03
Supraparticles of Au Nanorods by Spherical Confinement
Tian-Song Deng 1 Frank Smallenburg 1 Bart de Nijs 1 Thijs Besseling 1 Arnout Imhof 1 Marjolein Dijkstra 1 Alfons van Blaaderen 1
1Utrecht University Utrecht NetherlandsShow Abstract
Au nanorods (AuNRs) with roughly a width of 20 nm and a strongly tunable aspect ratio have attracted much attention due to their unique optical and electronic properties, which depend on their aspect ratio, shape, and size . Like spherical Au nanoparticles, AuNRs have the ability to absorb light of different wavelength ranges due to surface plasmon resonances (SPR). Due to the anisotropic shape of AuNRs, the SPR splits into two separate bands known as the transverse (TSPR) and longitudinal plasmon bands (LSPR). The TSPR is in the visible wavelength between 500 nm and 550 nm, while the LSPR varies from visible (600 nm) to near IR (>1200 nm), depending on the AuNRs aspect ratio.
The aim of our research is to study the packing of these AuNRs inside emulsion droplet; already this resulted for spherical nano-particles after droplet evaporation in a variety of supraparticles with intriguing icosahedral structures . Electron tomography is used for observing the 3D structures quantitatively on the single nano-particle level. Particles in the reconstructed structures were tracked by an algorithm which could find the position, orientation, and length of each AuNR . A thin shell of SiO2 was applied as coating on the AuNRs before emulsification. Such a layer has three main advantages. First, the total aspect ratio can be tuned by the SiO2 shell thickness. Second, a thin shell of SiO2 is useful to tune the LSPR of single AuNRs and the plasmonic coupling inside the supraparticles. Finally, a SiO2 shell also acts as a tunable spacer, which is helpful for the electron tomography and tracking, and for modifying the coupling of the plasmon resonances with other particles such as luminescent semiconductor particles that will be incorporated in binary supraparticles later.
The structures within the supraparticles highly depend on the aspect ratio of the AuNRs. When the aspect ratio is low (1.8), the supraparticles have a random packing of the nano-rods. However, supraclusters have a local smectic-like order when the aspect ratio of AuNRs is larger (e.g.: 4.7). With an increasing aspect ratio, one finds many more AuNRs organized side-by-side in 2D layers that themselves are stacked as well. This is consistent with computer simulations in which only a hard interaction between the rods and spherical confinement was taken into account.
Work is also in progress on the relationship between the structure and plasmonic properties of the supraparticles and on using these particles with sizes still in the colloidal domain in a second self-assembly step.
 C. J. Murphy, M. A. El-Sayed et al., The golden age: gold nanoparticles for biomedicine, Chem. Soc. Rev., 2012, 41, 2740.
 A. van Blaaderen, M. Dijkstra et al., Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement, Nat. Mater., 2014, ASAP, DOI: 10.1038/NMAT4072.
 A. van Blaaderen et al., J. Phys.: Condens. Matter, 2014, accepted.
3:30 AM - *PP5.04
Vivid, Full-Color Plasmonic Pixels
Stephan Link 1
1Rice University Houston United StatesShow Abstract
We show how vivid, highly polarized, and broadly tunable color pixels can be produced from periodic patterns of oriented gold aluminum nanorods. While the nanorod longitudinal plasmon resonance is largely responsible for pixel color, far-field diffractive coupling is employed to narrow the plasmon linewidth, enabling monochromatic coloration and significantly enhancing the far-field scattering intensity of the individual nanorod elements. The bright coloration can be observed with p-polarized white light excitation, consistent with the use of this approach in display devices. The resulting color pixels are constructed with a simple design, are compatible with scalable fabrication methods, and provide contrast ratios of at least 100:1. Compared to gold, aluminum is earth abundant, low in cost, compatible with complementary metal-oxide semiconductor manufacturing methods, and capable of supporting tunable plasmon resonance structures that span the entire visible spectrum.
4:30 AM - PP5.05
Exploiting Breathing Modes of Gold Nanostructures to Probe Solid-Liquid Thermal Interactions
Brian Donovan 1 John T. Gaskins 1 Ashutosh Giri 2 Patrick Edward Hopkins 1
1University of Virginia Charlottesville United States2university of virginia Charlottesville United StatesShow Abstract
Thermal transfer at the interface between solids and liquids is central to applications ranging from microelectronics cooling to targeted therapeutic heating. There has been a considerable amount of theoretical research on the thermal dynamics at solid-liquid interfaces, but experimental investigation has been limited by sensitivity constraints. Utilizing the well-known gold "breathing modes", or fundamental oscillations of thin-films and nanoparticles, we are able to analyze effects energy transfer from these solid structures to their environment. We use ultra-fast laser pulse excitation and environmental sensor configurations consisting of 20 nm gold thin films and nano-disks to excite fundamental oscillations in the gold structures and probe their changes in various environments. Using thin film sensors we have found that mechanical confinement of the gold surface by liquids can damp oscillations up to 60% and that despite being classically defined at highly wetting, the micro-mechanical properties of fluorinated liquids show limited mechanical interaction with solids on the nano-scale. To extend our analysis, we will use gold nano-disk sensors that exhibit lower frequency modes, enabling more sensitivity to other components of energy transfer at the interface. This combination of sensing configurations, all based on gold nano-structuring and ultra-fast pump-probe techniques allow us to deconstruct the mechanisms involved in transfer of thermo-mechanical energy from solids to liquids.
4:45 AM - *PP5.06
Stimuli-Responsive Plasmonic Nanostructures
Yadong Yin 1
1University of California, Riverside Riverside United StatesShow Abstract
Colloidal nanostructures of plasmonic noble metals (e.g. gold and silver) exhibit localized surface plasmon resonance and display significant scattering and absorption in the visible and infrared spectrum. The plasmon excitation of these nanostructures is strongly dependent on their size, shape, and the chemical environment. For anisotropic nanostructures, the exact plasmon resonance mode is also very dependent on their orientation relative to the incident light. Such dependence provides enormous great opportunities for developing novel stimuli-responsive colorimetric devices. In this presentation I will introduce some of our recent works in designing stimuli responsive materials by taking advantage of the orientational dependent plasmonic property of Au nanorods and the interparticle near-field plasmon coupling effect of one-dimensional Au nanoparticle chains.
5:15 AM - PP5.07
Hydrogen Sensing on Single Gold Nanorods by Surface Plasmon Spectroscopy
Michela Cittadini 2 Sean Collins 3 Paul Mulvaney 3 Alessandro Martucci 1
1Univ di Padova Padova Italy2University of Padova Padova Italy3University of Melbourne Melbourne AustraliaShow Abstract
The direct optical monitoring of electron exchange on single plasmonic nanoparticles (NPs), involved in chemical reactions with gas molecules, is one of the main challenges in the heterogeneous catalysis and gas sensing fields.
Catalysts are substances that speed up reactions by providing an alternative pathway with lower activation energy than that required for the uncatalysed reaction. A lot of research, both fundamental and applied, has been carried out to investigate how catalysts work and to increase their efficiency.
The present work shows how the use of Dark Field Microscopy (DFM) coupled with surface plasmon spectroscopy, enables the direct observation of the kinetics of H2 gas interaction with single gold nanorods (NR) coupled with Pt NPs. The plasmonic particles, gold NRs, act as optical probes, and enable the monitoring of the electron exchange through the measurement of their surface plasmon resonance (SPR) band shift. To improve the redox reaction kinetics, the Au NRs have been coupled with Pt NPs and embedded also into a TiO2 low scattering matrix. Both the Au NRs and the Pt and the TiO2 NPs have been synthetized by colloid chemistry. Several samples made of bare Au NRs, or Au NRs coupled with only Pt NPs or with Pt and TiO2 NPs have been deposited by spin coating on silica substrates.
The longitudinal Au SPR band shift has been monitored by DFM looking at the variation of the scattering spectrum of a single Au NRs in the presence of H2. Time-resolved measurements have been also conducted looking at the plasmon band shift, in wavelength, in order to monitor the kinetics of the H2 reaction. With such measurements it was possible to elucidate the importance of the adsorbed oxygen and the TiO2 matrix on the H2 reaction with the Pt NPs.
Wednesday AM, April 08, 2015
Marriott Marquis, Yerba Buena Level, Salon 2/3
9:30 AM - *PP4.01
Chemical Influences of Gold Nanostructures
Catherine Jones Murphy 1
1University of Illinois at Urbana-Champaign Urbana United StatesShow Abstract
Over the last several decades, the community of nanomaterial chemists have developed exquisite methods for creating gold nanostructures with controlled size, shape, and crystal form. As we move into the 21st century - "The Century of Biology" - biological applications of gold nanostructures abound, from chemical sensing to biological imaging to photothermal therapy. In this talk I will discuss some details in all these areas, and then show that the presence of gold nanoparticles in the extracellular matrix surrounding cells can lead to unanticipated effects; these effects could be used for good, if understood.
10:00 AM - PP4.02
Functionalized Nanoporous Gold: Synthesis, Properties and Applications
Monika Biener 1
1LLNL Livermore United StatesShow Abstract
Bulk nanoporous gold (np-Au) provides a robust materials platform to develop new functional materials by surface functionalization and templating. Nanoporous gold is also an ideal platform to study size effects as the characteristic length scale of np-Au can be adjusted from a few nanometers to several micrometers without affecting the overall 3D architecture (porosity and connectivity of the ligaments) by applying a simple annealing procedure. Both surface functionalization and templating of bulk nanoporous Au require coating techniques capable of uniformly coating ultra-high aspect ratio structures (aspect ratio of 104 for a 300 micrometer thick sample with 30 nm pores). This is the domain of atomic layer deposition (ALD) that in addition to uniformity provides atomic-scale thickness control by relying on self-limiting surface reactions. Our experiments reveal that even subnanometer-thick ALD coatings can stabilize the nanoscale morphology of np-Au up to 900 degree C while simultaneously improving the mechanical and catalytic properties. This, for example, opens the door for the development of gold-based catalysts for high temperature applications. ALD functionalized bulk nanoporous Au is also a very interesting platform to systematically study length scale effects in Li ion batteries. For example, it can be shown that by independently controlling pore size and the coating thickness of the active material (TiO2 in our study) one can achieve profound performance improvements by matching the Li+ diffusivity in the electrolyte and the solid state through adjusting pore size and thickness/phase of the active coating. For thin TiO2 films, supercapacitor like power performances can be realized.
Finally, by removing the Au core of ALD coated nanoporous gold, one can realize ultralow-density, ultra-high surface area bulk materials with interconnected nanotubular morphology. We demonstrated deterministic control over density (5 to 400 mg/cm3), pore size (30 nm to 4 micron) and composition. The materials are thermally stable and, by virtue of their narrow unimodal pore size distributions and thin-walled tubular design, ~10 times stronger and stiffer than traditional aerogels of the same density. Such low density foam samples open the door to more efficient (brighter) laser-induced nanosecond-scale x-ray (~ 5-10 keV) sources. Tests at the Omega laser have indeed revealed laser-to-x-ray conversion efficiencies between 5-10 % which are the highest conversion efficiencies that have been obtained from foam-based targets. The three-dimensional nanotubular network architecture also opens new opportunities in the field of filtration, and first experiments are currently performed and are very encouraging.
Work at LLNL was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344. Project 13-LWD-031 was funded by the LDRD Program at LLNL.
10:15 AM - *PP4.03
The Nature and Implications of Near-Perfect Nanoparticle Seeds
Chad A. Mirkin 1
1Northwestern University Evanston United StatesShow Abstract
Control over nanoparticle shape and size is commonly achieved via a seed-mediated approach, where nanoparticle precursors, or seeds, are hypothesized to template epitaxial growth. Despite the intimate relationship this suggests between seed structure and that of the final nanoparticle, structural control and characterization of the initial distribution of seeds are limited. We have found that an iterative reductive growth and oxidative dissolution process systematically controls seed structural uniformity. Further, we use this platform to study the implications of seed structure on: (1) the uniformity of gold anisotropic nanoparticles grown from them, (2) the ability to accurately determine physical properties of nanoparticles with well-established structures, and (3) the extent of ordering in nanoparticle crystallization. Importantly, this attention to seed uniformity improves noble metal nanoparticle uniformity and purity to unprecedented levels for eight different shapes produced from the same seed source, which enables particle optical extinction coefficient measurements and micron-size superlattice assembly.
10:45 AM - PP4.04
Reversible Assembly of Gold Nanoparticles from Mechanism Studies to Applications
Yiding Liu 1 2 Yadong Yin 1 2
1University of California, Riverside Riverside United States2University of California, Riverside Riverside United StatesShow Abstract
Assembly of gold nanoparticles (AuNPs) into one-dimensional structure is known to allow plasmon tuning due to the plasmon coupling effect. We here report a systematic study on the synthesis, surface modification of charged AuNPs, their reversible assembly into one-dimensional chain structures and applications based on this plasmon tuning process. The thermodynamics of the assembly process is evaluated by analysis of colloidal forces among AuNPs. It is revealed the key to control the assembly behavior is manipulation of these colloidal interactions, which provided driven force for assembly/disassembly process while ensured reversibility. Kinetics of the assembly process is also characterized by SAXS while memory effect of the assembly process is also studied by delicate control of assembly kinetics. The plasmon tuning by this assembly/disassembly of AuNPs is also applied in different applications. The as-assembled AuNP chains are able to be blended in polymers to form composite films. When external pressures are subjected to the composite film, the displacement of AuNPs associated with the deformation of polymer caused the disassembly of the AuNP chains and result in the distinct color change of the film. Thus, the composite film can be applied as colorimetric pressure sensor. AuNPs can also be encapsulated in nanoshells by a template synthesis method and reversibly assembled and disassembled in a confined space. This color-tunable rattle-type nanostructure can be applied as a chemical sensor in localized environment.
11:30 AM - PP4.05
Where Do The Hot Spots Between Two Plasmonic Nanocubes of Silver or Gold Form: Between Adjacent Corners or Adjacent Facets? A DDA Examination
Nasrin Hooshmand 1 Justi A Bordley 1 Mostafa A El-Sayed 1
1Georgia Tech Atlanta United StatesShow Abstract
Single Ag or Au nanocubes are known to be plasmonic nanoparticles with strong plasmonic fields which are concentrated around their corners. However, when these nanoparticles aggregate, they do so in a face-to face arrangement. The formation of hot spots between plasmonic nanoparticles in close proximity to each other is known to greatly enhance their plasmonic fields which is important in the field of imaging. Thus, what is the structural development of hot spots between two nanocubes in a face-to face dimer? Do they form between the corners or are they between the adjacent facets and what does this depend on? A detailed DDA simulation of Au-Au, Ag-Ag and Au-Ag dimers suggests that there is a competition between their formation in these two locations which depends on the inter-particle separation, the intensity, the wavelength and the polarization direction, of the exciting light (with respect to the dimer axis), It is also found that in the hetero dimer, the inter band electrons of the Au greatly quenches the plasmonic field of the Ag nanoparticles at short distances.
11:45 AM - PP4.05.5
Dealloying of Electrochemically Grown Au-Ag Nanowires
Loiec Burr 1 2 Ina Schubert 1 Wilfried Sigle 3 Christina Trautmann 1 2 Eugenia Toimil-Molares 1
1GSI Helmholtzzentrum fuuml;r Schwerionenforschung Darmstadt Germany2Technische Universitauml;t Darmstadt Darmstadt Germany3Max Planck Institute for Intelligent Systems Stuttgart GermanyShow Abstract
For the synthesis of highly porous gold structures, Au-Ag alloy is most suitable as starting material because it allows wet-chemical dealloying and has a complete solubility over the whole composition range . Nanoporous Au is characterized by an extremely high surface-to-volume ratio, and exhibits unique properties for applications e.g. in optics, catalysis, sensorics, and energy-harvesting .
The porosity of the material after dealloying depends on the initial Au:Ag concentration and distribution of the atoms. For Au-Ag alloys it has been experimentally observed  and theoretically discussed  that at the nano-scale, various processes such as oxidation, phase segregation and surface diffusion influence the final Au:Ag composition and distribution in the porous nanostructures. Furthermore, the initial size and geometry of the object also affect the final morphology.
In this work, we report the investigation of the dealloying process of Au1-xAgx alloy nanowires in an acidic solution as a function of initial wire composition and dimension, studying in detail the surface morphology and composition of the nanostructures before and after dealloying. We synthesize cylindrical Au-Ag nanowires with controlled dimensions (diameter: 25, 45, and 80 nm, length ~ 30 µm) and different Au:Ag ratios (60:40 and 40:60 at. %) by electrodeposition from a single-bath electrolyte in the cylindrical pores of etched ion-track membranes. After deposition, the polymer membrane is selectively dissolved and the released nanowires are transferred onto transmission electron microscopy (TEM) grids. The selective dissolution of silver in nitric acid leads to rough and porous nanowires depending on the initial Au:Ag composition. To gain a detailed insight into the dealloying process we investigate size, elemental distribution and crystallographic properties of the nanowires before and after Ag dissolution. A compositional analysis with high spatial resolution is performed by means of energy dispersive X-ray spectroscopy at a high resolution TEM.
Our results evidence surface segregation effects in Au-Ag nanowires which are not only size dependent but also strongly vary with the initial wire composition. Furthermore, the results indicate that surface segregation occurs on a time scale of days (< 3 days) independently of the wire dimensions. We also show that we are able to obtain highly porous nanowires with silver content below 10% and ligament size from 5 to 30 nm.
 ASM Internationnal, “ASM Handbook, Vol. 3: Alloy Phase Diagrams,” in ASM Handbook, 1991.
 A. Wittstock, J. Biener, J. Erlebacher, eds. No. 22. Royal Society of Chemistry, 2012.
 D. Belic#769;, R. L. Chantry, Z. Y. Li, and S. a. Brown, Appl. Phys. Lett., vol. 99, no. 17, p. 171914, 2011.
 L. Wei, W. Qi, B. Huang, and M. Wang, Comput. Mater. Sci., vol. 69, pp. 374-380, Mar. 2013.
12:00 PM - PP4.06
The Atomic Structure and Stability of Surface Facets in Gold Nanorods
Hadas Katz-Boon 1 Michael Walsh 1 Paul Mulvaney 2 Alison Funston 1 Joanne Etheridge 1
1Monash University Monash University Australia2Melbourne University Parkville VIC AustraliaShow Abstract
The ground-breaking discovery of surfactant templated growth of gold nanorods has inspired over a decade of research into the mechanisms that govern the shape of nanocrystals . Pivotal to shape control is the crystallography and atomic stability of different crystal surfaces. However, measuring these quantities on surfaces that comprise just a small number of atoms presents a new challenge. Using a quantitative analysis of the intensity in atomic resolution scanning transmission electron microscope (STEM) images , we locate and count atoms in gold nanorods in a time sequence. This enables us to determine the atomic structure and relative stability of each of the facets in a nanorod and to correlate this with its overall shape and size . We use this approach to measure and compare the dimensions and stability of low- and high- index facets co-existing in a gold nanorod . We also consider the stability of the overall shape and facet crystallography, in the presence of significant movement of individual atoms from one atomic site to another . This method provides insights into the relative surface energy of each of the crystal facets that are generated by, and collectively comprise, the overall chemical and geometrical environment of the nanorod
In this study, the gold nanorods were grown from small Au seed particles in the presence of cetyltrimethylammonium bromide (CTAB) and AgNO3  and the high angle annular dark field STEM was conducted using a double-aberration corrected Titan3 80-300 FEG-TEM operating at 300kV.
 Yu, Y.-Y., Chang, S.-S., Lee, C.-L. & Wang, C. R. C. Journal of Physical Chemistry B101, 6661-6664 (1997);
 Dwyer, C., Maunders, C., Zheng, C.L., Weyland, M., Tiemeijer P.C., Etheridge J., Applied Physics Letters100, 191915 (2012);
 Katz-Boon, H., Walsh, M., Dwyer, C., Mulvaney, P., Funston, A.M., Etheridge, J., submitted (2014);
 Nikoobakht, B. & El-Sayed, M. A. Chemistry of Materials15, 1957-1962 (2003)
12:15 PM - PP4.07
Gold/Silver-Polymer Hybrid Nanostructures as Thermoreversible Optical Sensors and Probes for the Quantification Radical Compounds
Eun Chul Cho 1 Ju A La 1 Sora Lim 1 Ji Eun Song 1
1Hanyang University Seoul Korea (the Republic of)Show Abstract
To date, so many excellent works have been reported for the applications of gold (Au) and silver (Ag) nanoparticles (NPs) to various fields. Meanwhile, combination of plasmonic NPs with functional polymers can further shed light on the characteristics of NPs. Here we will first present Au-hydrogel hybrid colloids as optical sensors in which multiple colors (maximum four colors: wine harr; violet harr; dark blue harr; faint blue) are switching reversibly in response to temperature changes. Spherical Au NPs are 2-dimensionally assembled on thermoreversible hydrogel NPs, and temperature-dependent swelling/shrinking behaviors of the hydrogel NPs in aqueous systems reversibly alter the assembly structures of Au NPs (packing density and interparticle distances) in the hybrid colloids. Accordingly, optical bandwidths of the hybrid colloids are reversibly changed with temperatures, and the bandwidth variations of the hybrid colloids are increased with the size of Au NPs (15 to 51 nm). With hybrid colloids assembled with 51 nm Au NPs, most optical signals are shown below 600 nm at room temperature while prominent optical signals are still recorded at 900 nm at 50 oC. Therefore, multiple colors are reversibly switched during repeated heating/cooling cycles.
Next, we will present the modification of Ag NPs&’ surfaces (nanocubes and nanospheres) with polyelectrolytes (either positive or negative) enables Ag NPs to use as probes for plasmonic-based, wide-range quantification of radical compounds. The quantification of radical compounds in a broad range with Ag NPs has been difficult due to nanoparticles&’ significant etching (high detection sensitivity) for a trace of radical. Through the modification, the polyelectrolytes protect the Ag NPs by probably either retarding (forming diffusion barriers) or preventing (blocking/entrapping/scavenging) the arrival of radicals to Ag NPs or both. The detection sensitivity (degree of etching) to Ag NPs by radicals and dominant mechanisms would be variable from the concentration and types of polyelectrolytes, respectively. The roles of the polyelectrolytes will be demonstrated by using radical compounds produced from tetrahydrofuran and H2O2. From the results, we could obtain calibration curves for the wide-range quantification of radical compounds. References: Lim et al., Chemistry of Materials 2014, 26, 3272; La and Cho, Analytical Chemistry 2014, 86, 6675.
12:30 PM - *PP4.08
Recent Developments in the Synthesis and Utilization of Gold Nanocages
Younan Xia 1
1Georgia Institute of Technology Atlanta United StatesShow Abstract
Gold nanocages are nanostructures with hollow interiors and porous walls. The smallest nanocages that we have been able to prepare are only measured 12 nm in size. By controlling the wall thickness, their surface plasmon resonance peaks could be precisely tuned to any wavelength in the range of 400-1200 nm. In addtion to Au-197, we have also been able to prepare gold nanocages from radioactive isotopes including both Au-198 and Au-199. This gives us a new opportunity to fabricate nanostructures for multimodal imaging applications. In this talk, I will discuss recent developments in the synthesis of gold nanocages, as well as their novel applications in imaging, sensing, drug delivery, controlled rlease, and catalysis.
De-en Jiang, University of California, Riverside
Dongil Lee, Yonsei University
Yuichi Negishi, Tokyo University of Science
Jie Zheng, The University of Texas at Dallas
Symposium Support World Gold Council
PP7: Optical Transitions and Electron Dynamics
Thursday PM, April 09, 2015
Marriott Marquis, Yerba Buena Level, Salon 2/3
2:30 AM - *PP7.01
Optical and Electronic Properties of Gold and Silver Metal Nanoclusters
Theodore Goodson 1
1Department of Chemistry, University of Michigan Ann Arbor United StatesShow Abstract
The discovery of metal nanoclusters (<3nm) has greatly expanded the horizon of nano-material research. These nanosystems exhibit molecular-like characteristics as their size approaches the Fermi-wavelength of an electron. The relationships between size and physical properties for nanomaterials are very interesting. Particularly, the changes in the optical properties have provided tremendous insight into the electronic structure of nanoclusters. The use of ultrafast laser spectroscopy on monolayer protected clusters (MPCs) in solution provides the benefit of directly studying the chemical dynamics of metal nanoclusters (core), and their non-linear optical properties. In this talk, the optical properties of gold and silver MPCs in the visible region are investigated using ultrafast spectroscopy. An emission mechanism for both the gold and silver nanoclusters is proposed based on both steady state and time resolved absorption and fluorescence up-conversion spectroscopy. We show that the nanoclusters behave differently from nanoparticles in terms of emission life-times as well as two-photon cross-sections. Further investigation of the transient (excited state) absorption has revealed many unique phenomena of nanoclusters such as quantum confinement effects and vibrational breathing modes. We have explored optical and electronic applications of these novel materials.
3:00 AM - PP7.02
Correlation of the Molecular and the Electronic Structure of Phosphine-Stabilized Au8-, Au9-, Au11- and Au14-Clusters
Frank Schiefer 1 Benjamin Sebastian Gutrath 1 Igor Beljakov 2 Velimir Meded 2 Wolfgang Wenzel 2 Ulrich Simon 1
1RWTH Aachen University Aachen Germany2Karlsruhe Institute of Technology Eggenstein-Leopoldshafen GermanyShow Abstract
In the last years phosphine-stabilized gold clusters with defined molecular structures, such as the well-known undecagold cluster of composition [Au11(PPh3)7Cl3], have attracted increasing academic and technological interest. Their unique properties arise from size quantization effects, leading to nonmetallic properties, exhibited by a nonzero band gap (Egap), which, in a first approximation, increases with decreasing cluster size and thus follows a simple scaling law. Hence, the ability to chemically access gold clusters with molecular precision and thereby to tune the electronic structure for the desired properties is of great importance for their applications in nanotechnology.
We have synthesized a series of triphenlyphosphine-stabilized gold clusters with a defined number of gold atoms, i.e. [Au8(PPh3)8](NO3)2, [Au9(PPh3)8](NO3)3 and [Au11(PPh3)7Cl3], in order to understand the interplay between structural features and the electronic structure. After crystallographic characterization of the full cluster structure including ligand shell, we assessed Egap by means of optical extinction spectroscopy, photoluminescence spectroscopy, voltammetry and density functional theory (DFT) calculations. Furthermore, DFT calculations on our newly synthesized gold cluster [Au14(PPh3)8(NO3)4] have been performed. A correlation of the characteristic energies derived from the experimental methods and DFT calculations revealed that the band gap does not follow a simple scaling law, but actually depends on the specific structural features of the clusters themselves as well as on charge effects of the cluster cores and the charge balancing counter ions.
3:15 AM - *PP7.03
Ultrafast and Temperature-Dependent Optical Properties of Monolayer Protected Quantum-Sized Metal Clusters
Ramakrishna Guda 1
1Western Michigan University Kalamazoo United StatesShow Abstract
The research on atomically precise monolayer-protected metal clusters has captivated the imagination of chemists, physicists and material scientists for the last ten years both for fundamental science and applications in catalysis, sensors and optoelectronics. Unique optical properties were observed from these clusters that show discrete electronic states and interesting luminescence properties. These properties are dependent on core size as well as on crystal structures. Our research efforts are focused on understanding the role of core-gold and shell-gold interactions on their optical properties. Ultrafast luminescence measurements have focused on understanding the relaxation of core-gold states while temperature-dependent optical properties were used to understand the interactions of core-gold and shell-gold. In this presentation, ultrafast luminescence and temperature-dependent optical properties of Au144, Au102 and Au67 would be discussed. The results show that the structure and symmetry of clusters are crucial for understanding their optical properties. New results on ultrafast luminescence and temperature-dependent optical properties of Ag44 and Au22 would be presented that have shown contrasting behaviors.
3:45 AM - PP7.04
Effect of Spin-Orbit Coupling on the Optical Absorption of the Au25 Cluster
De-en Jiang 1
1University of California, Riverside Riverside United StatesShow Abstract
Because of their molecular-like properties, ligand-protected gold nanoclusters have well-defined UV-vis or optical absorption bands. These bands are very characteristic and often used a fingerprint to identify different clusters. Therefore, an interesting question would be if the spin-orbit coupling could be reflected in the UV-vis absorption spectra of ligand-protected gold nanoclusters. A straightforward approach to this question is to compute or simulate the optical absorption spectrum for a specific cluster by comparing two models: with spin-orbit coupling and without. Then one compares the simulated spectra with the experiment. In this talk, we will discuss the effect of spin-orbit coupling on the optical absorption of the most widely studied thiolated gold nanocluster, Au25(SR)18-. We will show that the ubiquitous shoulder peak or the double-peak feature below 2.0 eV of Au25(SR)18-&’s optical absorption is due to spin-orbit coupling. We will further discuss the many implications of this finding.
4:30 AM - *PP7.05
Synthesis, Optics and Applications of Plasmonically Coupled Nanostructures
Jwa-Min Nam 1
1Seoul National University Seoul Korea (the Republic of)Show Abstract
Designing, synthesizing and controlling plasmonic nanostructures such as Au and Ag nanoparticles with high precision and high yield are of paramount importance in optics, nanoscience, nanobiotechnology and materials science. It is particularly important and challenging to generate and precisely control plasmonically coupled nanostructures with ~1-nm plasmonic gap for larger signal amplification and more quantitative signal output. Here, I will describe various functional molecule(e.g., DNA, protein, polymer, etc)-based synthetic strategies to build up new types of plasmonic nanoprobes with high structural controllability. The use of these plasmonic nanostructures including plasmonic nanogap structures and anisotropic nanostructures as excellent optical signal enhancement and biosensing platforms in detecting biomolecules sensitively, quantitatively and specifically will be mainly shown and discussed.
5:00 AM - PP7.06
Stimuli Responsive Gold Nanoclusters and Distance Dependent Photophysical Properties of Silver Nanoclusters
Anil Desireddy 1 Eva Balog 1 Saumen Chakraborty 1 Andrew Shreve 2 Reginaldo Rocha 1 Jennifer Martinez 1
1Los Alamos National Laboratory Los Alamos United States2Univ of New Mexico Albuquerque United StatesShow Abstract
Nanoclusters are comprised of stable collections of small numbers of metal atoms (e.g. gold or silver, 2-144 atoms, le; 1.8 nm) that can have intriguing catalytic, magnetic or photophysical properties. Nanoclusters bridge the gap between atoms and nanoparticles, and exhibit unique physical and optical properties not seen in bulk materials due to quantum effects. Nanoclusters possess superatomic orbitals similar to atomic orbitals, where each atom of the nanocluster accounts for their properties, and where addition of an extra atom to a cluster completely changes its physical and optical properties.
Recently biomolecule templated metal nanoclusters have gained much attention due to their potential biological applications. Genetically encoded polymers (i.e. elastin like polymer (ELP)) consist of repeating units of sequence yielding a polymer with defined stimuli responsive, biocompatiblity and programed assembly. For the first time we report the direct synthesis of pure, single sized, stimuli responsive, water-soluble and biocompatible ELP templated Au nanoclusters. The polymer design, synthesis protocol, optical properties and electron microscopy and stimuli-response will be discussed.
Fluorescent nanoclusters, in particular DNA templated silver (Ag) clusters, have drawn much attention, as they have tunable fluorescence emission, single-timescale photoblinking, high quantum yields, and thus have large potential for applications in bio- imaging, sensing and for energy harvesting. Toward energy harvesting we have begun to assemble clusters, through DNA hybridization, and monitor their energy. We will discuss the synthesis, characterization, and photophysical properties of assembled silver nanoclusters.
5:15 AM - *PP7.07
Toward Understanding the Growth Mechanism and Luminescence Fundamentals of Thiolated Gold Nanoclusters
Jianping Xie 1
1National University of Singapore Singapore SingaporeShow Abstract
Despite 20 years of progress in synthesizing thiolate-protected gold nanoclusters (or thiolated Au NCs), the knowledge of their growth mechanism and luminescence fundamentals still lags behind. Some of our recent work may shed light on these issues, and will be discussed in this presentation. In the first part, we will discuss the detailed growth process of thiolated Au NCs by tracing all stable intermediate species from reduction of Au(I)-thiolate complexes to evolution of thiolated Au25 NCs (J. Am. Chem. Soc.2014,136, 10577). In the second part, we will discuss some fundamental issues on the luminescence properties of thiolated Au NCs, including the origin of emission and the size effect in luminescence. We will focus our discussion on a possible mechanism of aggregation-induced emission (AIE) of the Au(I)-thiolate complexes on the NC surface (J. Am. Chem. Soc. 2014,134, 16662). We will also extend the concept of AIE to a recently identified, highly luminescent thiolated Au NC, which has a precise molecular composition (Au22(SG)18) and structural information (J. Am. Chem. Soc. 2014,136, 1246).
5:45 AM - PP7.08
Highly Luminescent Au(I)-Thiolate Coordination Polymers
Aude Demessence 1 2 Christophe Lavenn 1 2 Larysa Okhrimenko 1 2 Nathalie Guillou 3 4 Miguel Monge 5 Gilles Ledoux 1 6 Alexandra Fateeva 1 7
1Lyon 1 University / CNRS Villeurbanne France2IRCELYON Villeurbanne France3Universiteacute; de Versailles Saint-Quentin-en-Yvelines / CNRS Versailles France4ILV Versailles France5Universidad de La Rioja Logrontilde;o Spain6ILM Villeurbanne France7LMI Villeurbanne FranceShow Abstract
Polynuclear hybrid Au(I) compounds exhibit a very large domain of applications such as electronic devices, contrast agents, sensors or photocatalysts. All these applications are related to the ability of gold(I) to form aurophilic interactions which give luminescent materials. Among hybrid gold species, gold(I) thiolate compounds are an important class of materials due to the high affinity of gold for sulfur atoms that can generate molecular complexes, extended polymers, stabilized gold nanoparticles or self-assembled monolayers. Thus in nanoscience, gold(I) thiolate polymers are a key step in the Brust-Schiffrin synthesis of functionalized gold nanoparticles. However relatively little is known about the relationship between the structure of the Au(I)-SR intermediate and the formation of the nanoparticles. In addition, the luminescence of gold thiolate nanoclusters, with gold core diameter less than 2 nm, is highly dependent of the structure, the arrangement and the length of Au(I)-thiolate motifs at the surface. So to understand the formation of gold thiolate nanoparticles and clusters and also to explain the luminescence of gold thiolate coordination polymers and clusters, we will present the syntheses and the first structure resolutions, by powder X-Ray diffraction, of series of [Au(I)-SR]n compounds. We will demonstrate that depending on the substituent (R = Ph, PhCOOH, PhNH2) different structures are obtained: lamellar, helicoidal or cyclic. The photophysical properties governed by aurophilic inetractions and Ligand-to-Metal Charge Transfer are studied by room temperature and solid-state emission and lifetime decay experiments, and are explained by DFT calculations. Among those coordination polymers, two exhibit dynamic OFF/ON emission switching, one associated with an irreversible solid-state thermal crystallization and the other one from a reversible esterification. In addition we will show, from those preformed coordination polymers, that exchange reactions of thiol ligands involve dissolution/recrystallization mechanism, pointing out that each thiolate ligand induces its own polymeric structure.
 Schmidbaur H., Schier A., Chem. Soc. Rev., 41, (2012), 370.
 Lavenn, C.; Albrieux, F.; Tuel, A.; Demessence, A., J. Colloid Interface Sci., 418, (2014), 234.
 Luo Z., Yuan X., Yu Y., Zhang Q., Tai Leong D., Yang Lee J., Xie J., J.Amer. Chem. Soc., 134, (2012), 16662. Das A., Li T., Li G., Nobusada K., Zeng C., Rosi N. L., Jin R., Nanoscale, 6, (2014), 6458.
PP8: Poster Session II
Thursday PM, April 09, 2015
Marriott Marquis, Yerba Buena Level, Salon 7/8/9
9:00 AM - PP8.01
Anisotropic Gold Nanocrystals Obtained via Chemical Vapor Deposition
Sohini Manna 1 2 E.E. Fullerton 2
1University of California San Diego La Jolla United States2Center for Magnetic Recording Research La Jolla United StatesShow Abstract
Use of nanostructures in various applications such as biodetection, catalysis and drug delivery has led to the need for faster and more controlled synthesis routes. Recent advances have been made which allows the production of nanostructures with control over particle size, shape, and composition. These architectural parameters dictate the resulting physical and chemical properties. In particular the extraordinary optical properties of such nanostructures can be used in a variety of highly sensitive chemical and biological detection schemes, and may also find use in novel, nanoscale optoelectronic and photonic devices. The majority of the recent efforts has focuses on isotropic, pseudo-spherical structures using chemical synthetic routes. We report a simple thermal chemical vapor deposition route to produce single-crystal Au nano-crystals without using any external catalysts. Heating AuCl3 precusor in a furnace above 450C in an argon environment with Si (100) substrates leads to the formation of Au nanostructures like prisms, triangular plates, decahedrons, icosahedrons and hexagons which grow vertically on the Si substrates. We observe a fine interplay of reduction of surface energy vs internal stress, which plays an important role in the morphology of gold nano-crystals. The strain distribution is influenced by the Au-substrate interface and Au-air interface, which arise due to differences in their thermal expansion. We have studied the growth and properties of singe crystal anisotropic gold nano-crystals by utilizing synchrotron based coherent diffraction imaging to study these nanostructures along with other traditional characterization techniques like XRD, EDX and AFM. We find the lattice strain at the surface of the octahedral nanocrystal agrees well with the predictions of the Young-Laplace equation quantitatively, but exhibits a discrepancy near the nanocrystal-substrate interface resulting from the interface. Application of this approach to the growth of other metallic nanostructure will be discussed.
Research at UCSD support by NSF DMR Award # 1411335.